Don't see the point in these sort of list topics. I persoally am not going to read a list of numbered letters and numbers.
I should say that combining drugs is hit and miss and potentially more dangerous than any drug on its own. Noone really knows what any of these chemicals are truly doing to us. No one knows how they are metabolically reacting together. Of course, we can infer their action from other similar drugs but we should all be doubly careful when doing combinations. Ensure you are familiar with all drugs in isolation, ensure that you understand how they act on the brain and how the body metabolises them to avoid stacking drugs that have possible enzymatic or neurological similarities. MXE, for example, should probably not be combined with quite a number of drugs, at least speculatively.
Anyway, limiting to 2 drugs is something I basically never do. I would say the last 30 psychedelic experiences I have had have been on a psychedelic (maybe two), perhaps a dissociative at some point, always cannabis and often GHB and/or opiate. The opiate and cannabis are daily anyway so I just happen to be on them when tripping I suppose.
A great combo is 2C-D + DMT. Utter raving madness, hysterical laughter, etc. Very alarming and hyper but every little puff of DMT is like inhaling a volcano. Good times!
4-ho-MET + MXE always got me good. Made the MXE less mechanical feeling. I feel like these two work well, mainly because I like the way their names look together.
DMT + (anything but) nitrous oxide requires finesse of timing but if you succeed in stacking the peaks, you may very well turn into some kind of food item. I was a sandwich.
GABAergic + 5-Meo-DMT is a requirment for me. 5-meo-DMT terrifies me, and the physical reaction is too strong for me to enjoy it but a mild-to-mid benzo dose or GHB can assist. It can also lead one to a false sense of security and certainly only slightly reduces the panic.
For other drugs, a great combo is 20-30mg of dexamp, 1-2g GHB (repeated) and maybe either opiate or dissociative, all quite low dose. Perfect drugs for doing stuff like living life and whatever on. Easy to get into a habit of this sort of multi-drugging given that all of these are addictive, so this is something that should not be done too often. For me, its a few times a week and I think that's too often.