Yes, POTLUCK is a Scrabble word!

Letter values in Scrabble US: P 3, O 1, T 1, L 1, U 1, C 3, K 5.

Is it a valid word?

POTLUCK is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

whatever happens to be available especially when offered to an unexpected guest or when brought by guests and shared by all