I think Gravity Aided's suggestion is the best, or maybe 'accounting irregularities'.
My mate used to work at an airport food outlet where several senior staff were doing this. Even at manager and assistant manager level, the pay in these kinds of jobs isn't that great, so in a job where cash handling is routine, it's easy to significantly boost pay by taking a few large notes a day. At a lower level (i.e. my mate), the workers used to barter with other food outlets (e.g. some cookies for a big mac).