Similar to game plan, it's the idea of figuring out what you're going to drink at parties/bars/events.
Availability of the drinkplan may be based on levels of monetary fundage.
Can be used to denote how MUCH one will drink at a party/bar/event.
"Hey man, what's your drinkplan for New Year's Eve?"
"Oh man, I get paid on the 2nd, I only have a $20. I'm thinking a 30'a Stroh's or a buncha tallboys'a Molson, eh?"
"Hey dude, how much you gonna drink tonight? What's your drinkplan?"
"Heavy and often, like my sex."