DO NOT, I REPEAT, DO NOT, MIX PSYCHEDELICS WITH METH...especially if you're doing large doses or using the needle (the needle itself can make you see crazy shit...you don't want any tryptamines which are nearly the 5-HT molecule itself to send that mind into dark places). That is a good way to schiz the fuck out and completely lose your shit.
Don't take any other stimulants or same shit would happen...even pseudoephedrine is a big mistake on meth because of additive sympathomimetic effects which will overload your ass with stimulation.
The only thing I recommend to supplement meth with are CNS depressants. If you like opioids, they're a good mix. Benzodiazepines are a god-send for comedowns, and assuming your tolerance to them isn't too high/you haven't way over done it with the ice, can help with any apprehensive, anxious, or paranoid feelings.
Cannabis, for most, will make you super fucking loopy if done towards the end of meth's effects. I remember getting home after taking the ACT after being up for 3 days vaping it, and siting in my car in the garage smoking a bowl. It took me like 3 hours to smoke that bowl and the walls going into the house wear breathing and all sorts of shit.