Fill (one's) boots British informal
To take as much as one can
People tend to fill their boots, when eating at the buffet.
To replace someone's position, which comes fromt the idea that one's wearing the other person's shoes
If you do not try your best, he will fill your boots soon.
To obtain something or gain the right to access to a certain location or object via deception
The verb "fill" should be conjugated according to its tense.
A source says that It originated with 'The Tinder-Box' by Hans Christian Anderson (1835), where the soldier not only stuffs his pockets with money but also his hat and boots.
A legal matter that is very easy to solve
The house owners didn't lock the doors before going out, and that's why they got broken in. This is an open and shut case.