I'll throw my two cents in regarding the most well known "classical" psychedelics (although as stated by Solipsis and others it's hard to define and depends largely who you talk to).
Srooms, Cacti, Ayahuasca/DMT, and LSD(maybe LSA but I feel it's less common in the popular consciousness these days idk) are the ones that I think of when I hear the term 'classical psychedelics' as it relates to my perception of the general consciousness about these things, but this is very subjective.
'Classical' psychedelic combos for me: LSD and DMT, Mescaline(T. Bridgisii mostly but some S. Pedro and some various forms of extracts) and DMT, LSD and Shrooms, LSD/LSA and Mescaline, none of which are really sandwiches per say but I find with the all encompassing ones like good Bridgesii or a solid dose of L or shrooms can be enough of an experience on its own and adding other strong things into the mix can be confusing or distracting or just unwanted. Also there is something to say regarding taking plant based entheogens in their whole form or reduced to a tea and the fact that you are actually taking a combination of alkaloids which have been synthesized by the earth into the particular plant. So by eating cactus you really are essentially taking a fat 'psychedelic (p)sandwich' albeit one which has been designed by the ultimate biochemist, Nature.
Now to some of what I consider 'classical' psychedelics although it includes some well known and somewhat studied novel compounds, mostly coming from pihkal and tihkal
-Broadened 'classical' psychedelic combos: 2C-E and 2C-T-2(caution with this one, although I and my friends had no ill effects), 2C-E and LSD, 2C-E 2C-T-2 and LSD, also DMT with all previous combos and I almost forgot 4-HO-MET and 5Meo-MiPT(4+8 spaced out which was surprisingly lackluster compared to just 8mg of meow mipt all at once). All of these particular combos produced wonderful and unique experiences with a very special synergy between different things. As long as the durations or peaks line up fairly well it usually is a good combo, that is of course once it's been confirmed that there are no contraindications between the things you are taking (google helps). As stated previously nature is the best biochemist and we have studied the molecules that have been given to us and then we have altered them through our progress in chemistry, which is where guys like Shulgin and Nichols (and many many more) have done great work exploring novel substances. After combining multiple phenethylamines as well as combining tryptamines, I had the thought that maybe these novel 'research chemicals' may actually exist in very small amounts in plants. We know that T. Bridgisii is chalk full of alkaloids and have been able to isolate and study the main ones (mescaline particularly, giving us the 2cxs and maybe the Doxs I believe). Mushrooms also have been shown to have different compounds from psilocybin to baestyricin(sp?) and who knows what else. This assertion is not yet based in any truly scientific findings but merely an idea that developed over several years and experiments. I found when combining 2cs they seemed to come closer to a full cactus experience, but maybe with less delirium/intoxication(my best Bridgisii experience had me dissolved into everything in a state of blissful Catatonia for many hours,just engulfed by deep red and yellow expansive fractal visuals, which was then realized to be a manifestation of my past and future). Now when you throw the L in the mix things start getting interesting as the L has its own very unique character and the milder colors of the 2cs get saturated by the LSD rainbow and this produced a ++++ for me, one of a special few experiences including the Bridgisii exp above. The 2ce+2ct2+lsd had me become a star of fantastic light and brilliance and then slowly lost myself into everything as I focused on these massive dancing entities conveying information through their insane psychedelic dance.
Now let's get to the weirder stuff and add in some other goodies (NOTE SOME OF THESE COMBOS ARE DANGEROUS AND COULD RESULT IN BODILY HARM, UNCONSCIOUSNESS, BLACKOUTS, BAD VIBES, and possibly DEATH! All harm reduction techniques should be adhered to as much as possible to reduce these risks because no one wants to actually die on any drug, so take these with a grain of salt and know that they have almost strictly produced less than 'pleasurable' effects)
You can throw nitrous in with all of my afore mentioned combos as I have had my share of n2o on almost every psychedelic I have done (although the nature of nitrous prevents most of the recollection of said experiences and is more catagorized in my mind as one big chaotic blur of a memory), also varying forms of thc of course which can drastically change a trip.
In fact one of the most terrifyingly intense experiences, which I don't plan on repeating, was with weed, Bridgisii, vaporized DMT, and two n2o balloons. It did not help that as soon as I hit the nitrous some sirens started going off down the street but they were so loud it felt like it was everywhere and in my head and I was blasted into hyperspace with an even more anxious vibe than normal because of the sirens persisting for the majority of the experience, although they quickly became symbols for other concepts and warped and pitched weird in combination with the auditory hallucinations often experienced on DMT. I attempted a lighter version of that with just nitrous and DMT, since they both have short durations but it didn't prove to be that fun because my head felt like a balloon and it expanded and contracted as I breathed in and out, I also felt like I was entirely blue from head to toe and that surely I was suffocating from the nitrous and I was gonna die like this. Thankfully I did not since the body tends to take care of itself especially when in hyperspace(I never think about breathing or remember to breathe but somehow it happens) and it was the ego death coupled with the 'possibility' of suffocation. Also DCK and 4HO-MET was the most chilled out and visually stimulating combo I have taken in a while. It produced nice visuals and profound color enhancement and visual acuity. It felt at times as if I could see everything clearer than ever, which was cycled back and forth with everything warping and turning with the fractals.
The final thing I'll throw in here since it's getting long is my one and only DXM/DPH and Nitrous combo, which was reckless, impulsive and dumb. I won't go into details because I can't, considering I don't remember most of the experience. However I did have a sober (mostly sober, he just smoked weed) trip sitter who is very well versed in this arena (we have explored a lot of these substances together), and had I not had a sitter, I am sure I would have been in jail or the hospital or even died. It was very delirious and the dxm/dph presented realistic hallucinations unlike anything I have experienced. Almost like a dream, but a dream where you have no mental capacity or control, so basically the opposite of a lucid dream. The nitrous didn't help as I compulsively did them back to back from a proper canister until I ran out and at some point I passed out on my friends couch only to awake in a confused panic with strong amnesia peppered by little flashes of what had happened. Not something I suggest anyone go for and it is one of the few true regrets I have from taking drugs, although it did teach a valuable lesson and was not particularly psychologically scarring because I was way too fucked up to remember anything and mostly felt embarrassed that I behaved like an ass in front of anyone, although it's not so bad since it was in a controlled environment and only around my best friend so we had a good laugh about it once I recovered fully.
So it is of utmost importance to act with care and knowledge when mixing things. Make SURE to the best of your ability that taking two things isn't gonna kill you, and if you are suspicious at all DO NOT TAKE THE RISK! There have even been deaths from some psychedelics based on their pharmacological action alone (nbomes, aMT, etc) without combinations so it's very hard to say what's safe. If one finds two or maybe three things that have good safety profiles and history of use and decides to mix them, one should probably take significantly less of each than you would expect. Like for 2ce on its own I've gone as low as 5mg and as high as 40mg(not very fun) but tended to stick with the 10-20 range. When adding the 2ct2 it would typically never go above 20 cumulative and more typically would be like 5+5, 6+6, 8+8, as well as other ratios(8 2ce and 4 2ct2 was a favorite ratio of mine). Synergy is unpredictable especially when mixing different classes of chemicals so always dose lower than expected, much like what Solipsis said.
As a general rule of thumb for me I try to mix a solid classical psychedelic that I know is not likely to have adverse health reactions, and add little bits of other items which I know I tolerate well to spice and flavor the experience to whatever I'm going for but try to avoid redundant effects (mescaline and 2ce for instance as they are so similar and could lead to overstimulation, although I'm sure it would likely still be a great experience given the right setting). And realistically one should keep it to no more than 3(although I've broken this rule when adding things like weed, Kratom or nitrous) because still so little is known about interactions.
Don't dive blindly into combos because many a diver as found the water to be shallow, make sure you measure everything first. It's also a good idea to know each chemical individually and how you respond to different doses and changes before mixing two or more things together.
Still hard to clearly define and maybe we shouldn't stress TOO much over what counts and doesn't count... After obvious ones like mushrooms or LSD, IMO 2C-E should be a good example because it has potent psychedelia, is not limited to say one of the senses, has broad potential... Things like bufotenine and harmine on the other hand seem useless for mostly any generalization on this part as far as comboing is concerned.![:\](https://bluelight.org/xf/BL_Images/Orig_Emoji/wrygrin.gif "wry grin :\")
that could be fixed if you tell us what aspect of your question and this discussion you wanna focus on, we could help steer in some direction ;P
