^^i'm gonna have to go with cannabis and any drug as a good combo... ...
i remember a few years back being on either eth-lad or 1p-lsd and i had a bag of 5meo-dmt. i was used to taking like 20mgs or so of the dmt and it didn't really do too much for me... but this time i was pretty fried on whatever chemcial i was on, the 1p or eth-lad, so i decided to dip my finger in the 5meo-dmt and take that orally... i was walking around my house and after about a half hour after taking the dmt, i was like, i have to sit down. i was sitting on the floor and it was like a magic carpet ride, kind of like being drunk with the spins except i was moving forward. i was traveling through all of this light and paintings. it was pretty cool. the come down felt like i was sick with the flu or something with out the stuffy nose and cough, but it was a pretty cool high. i only took about 5mg or so, the acid made it way stronger. i've never felt drunk from any type of acid either. it's usually the opposite.
also i never took a real hit of salvia while peaking on any kind of acid, but i used to take a pinch between my fingers and burn that and inhale it like incense. it didn't make me break through to the salvia world at all, but it would warp the air like i was in a fun house with those crazy mirrors. it was pretty cool. that never happened on salvia alone... one time i took a full rip of salvia at the end of an acid trip, trying to break though, but all that happened was light was flashing. i think the fact i was coming down from the acid made the salvia not work 100% cause of tolerance. i don't know.
also nitrous oxide and shrooms or dxm. i heard lsd is great, but i never tried it. shrooms was probably the craziest that i tried with nitrous. the nitrous hit like paralyzed me and my friend that recommended the drugs to me, his image was like trapped in my head, he was covered in dirt like he was burried in the ground, there was all sorts of crazy yellow light peaking through the dirt with my friend just stuck at the top of my skull. i'm not sure if it was closed or open eyed visuals. lol. for whatever reason, i found this to be enjoyable.... when doing nitrous on dxm,i always just got trapped in the color red, if that makes any sense.
i'm editing this to say sorry if this isn't synergy and just added effects. i looked up synergy and thought my post made sense, but i just noticed the "added effects" after i posted. maybe this is considered added effects. i don't know. sorry if this is out of place for your topic.