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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
by Full Boots May 01, 2005
 
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!
by dean shannon March 07, 2007
 
3.
an invitation to eat as much of whatever is offered as you want and take some home with you. the phrase may come from a time when inviting travelers into your home to share a meal was more common. it was considered polite to eat your fill but not to also fill your bag with food for later. the invitation to "fill your boots" would be permission from the host to do so.
host: there is more here than we can all eat now, feel free to fill your boots.
guest: thanks mister, that's generous of you.
by no one of importance June 21, 2012