Masturbating on a combo of opioids and amphetamines is so good it scares me a bit. I avoid taking advantage of this combo too often, because it kind of ruins sober sex and masturbation for me. I can go for hours (with plenty of lube) and if I time it right, the orgasm is overwhelmingly intense.
Amphetamines alone make for a good wank, but I don't last as long as I'd like to. Opioids alone can be really good if I'm really horny, but my libido isn't always strong enough to really get into it. Too high of a dose also makes it nearly impossible to cum, and even if I do, sometimes it's not very pleasurable. But the combo of the two pretty much cancels out the downsides of both.
As for specific drugs, the best combo I've experienced is meth and fentanyl. The opioid I use doesn't seem to matter as much as the choice of amphetamine, though - hydrocodone, oxycodone, fentanyl analogues, and heroin all work just fine. I prefer fent and fent analogues mainly because they are easy to dose intranasally when dissolved into saline nasal spray, which kicks in quickly and consistently. It also doesn't last super long, so if I overshoot the initial dose, I can just take it easy with redosing and let it wear off in time for an earth-shattering orgasm. Regular old amp works reasonably well, but meth is definitely better thanks to the much stronger euphoria. I've never tried any other RC amphetamine analogues (either for masturbation combos or in general).
Throwing in a very small dose of dissociatives can work surprisingly well, although obviously too high of a dose doesn't work well at all. One of the countless reasons I miss MXE :'(
I'm actually not a huge fan of wanking on psychedelics, even though they're my favorite class of drugs in general. I get distracted easily, and it doesn't seem to add much to the experience. Seems like they would combine better with actual sex, but I have yet to have an opportunity to test that theory.
I pretty much always smoke weed before masturbating or having sex, but I hardly even count that as a drug - and I'm a bit of a pothead, so I smoke weed before, during, and after most activities, sexual or otherwise
