I used to enjoy mixing these drugs:
Cannabis and LSD.
Cannabis and low doses of pharm opiates like 5mg of oxy, a low/moderate dose of codeine, or 5-10mg of hydro.
Cannabis and alcohol. Just be careful not to drink way too much in a bar or party setting.
I tried mushrooms, cannabis, and nitrous all at the same time and that just made things confusing and not enjoyable.
Now I don't use anything but if I were going to I just would take a low dose of mushrooms, or maybe eat a weak edible made with cannabis or hash.