LUKE: So you get unpacked?
JESS: Yup.
LUKE: Get enough space in the closet?
JESS: Plenty.
LUKE: You hungry?
JESS: Eighteen.
LUKE: What?
JESS: Just counting how many questions ’til we hit twenty.
Jess is referring to Twenty Questions, an American parlour game originating in the 19th century. One person chooses a particular object or subject, but keeps it a secret. Players take turns asking them questions about it, which can only be answered by “yes”, “no”, and “maybe”. Winning the game involves correctly guessing the answer within twenty questions – if not, the answerer wins the game. Twenty Questions has been made into several successful radio and television quiz shows.
Of course, Luke isn’t trying to guess anything, just asking if Jess has everything he needs, but Jess is clearly not in the mood.
The Annotated Gilmore Girls 