Its gotta be weed. I got the movie on my PC and he says they have:

2 bags of grass
75 pellets of mescaline
5 sheets of high-powered blotter acid
salt shaker half full of cocain
a whole galazy of multicolored uppers, downers, screamers, laughers
quart of tequila
quart of rum
case of beer
pint of raw ether
two dozen amyls

It must be weed, I'm pretty sure that is the only smokeable thing he lists, 'cept coke i guess but you probably wouldn't use it that way. And for me, I don't see that scene having any hallucinations, when he floats on the couch, to me it describes the feeling of being high, like your in your own little world, that scene describes getting high for me very, very well.

So: its weed... and I don't think they picked up any more drugs at that point in the movie, but he did get some adrenaline later on, so assuming they only had what they listed at that point, it was weed.