What is Fill Your Boots?
1.
An invitation to partake with gusto, as in "be my guest," or "help yourself."
Here's one for you to chomp on, fill your boots
2.
1. Invite another to help themselves to their optimal capacity or
2. Attempt a difficult task or ordeal.
1. HE: Are these sweets free?
SHE: Fill your boots.
2. HE: I'm going over there to crack on to Naomi Campbell!
SHE: Fill your boots!