Pitch

Verb: to contribute money towards the purchase of alcohol (or weed, etc.) or to reimburse someone who has already made the purchase

“Let me know how much you need me to pitch for the booze for tonight”
“Hey man thanks for sharing your weed, do you need me to pitch at all?”

Pull

Noun: a person who can be relied upon to regularly supply alcohol, especially to underage drinkers
Verb: the act of buying alcohol for someone who is underage

“Don’t worry, I can get us some vodka for tonight, I just have to call my pull”
“Do you think your older sister would pull for us?”