Asking the waitress for a bunch of blank receipts (or sometimes stealing a bundle) so you could write out your own meal check and spend the money on more worthwhile things like cheap food and a few drinks.
A friend actually went into a print-shop and ordered a batch of custom printed receipt books. He went back and it was a whole pallet of them they'd printed! Big job though, so the guys "ate" at the same "restaurant" for the full duration.
Losing fuel receipts and not getting paid for filling the van/truck.
Getting put into really nasty accommodation by the company because it was the cheapest the office staff could find....