UV flashlight to check bills. Every store should have one, but they're pretty cheap JiC yours doesn't. Like 10 bucks.
I used to carry my own box cutter since most of the time the store's cutter is duller than plastic knives on the condiment bar. Something like
$1 is cheap, small, clips to your pocket.
I guess it depends on the store, but I always wore a watch, almost always a GSHOCK with multiple alarms (to keep track of breaks/tasks/shift changes/etc), stopwatch, and hourly chime. Barring wearing a watch, a small portable alarm clock with a clear, easy-to-read face.