None. Vit C is quite good for you in general and moderation though. But not for tripping. Or pills/MDMA or owt else of interest. An open mind is all that is of any real use before taking any drug of any description, no? Supplements tend to do more harm than good whichever chem you're chomping, in my opinion.
What are you planning on taking and what ickies are you thinking on combining it with? Most combos are fairly harmless beyond pointlessness but the odd few are pretty dangerous so best to be informed really.
Some things like Quercetin or Chamomile are thought to inhibit certain enzymes that may potentiate/enhance the trip in some way. I've tried both with mushrooms, and it seems to extend the peak for a bit.
i prefer to keep healthy foods around for during the trip-- like trail mix or fresh fruits. taste hallucinations while tripping, combined with making sure you stay hydrated and energized to take on the world!