While I was in college I worked in a 7-11.

The nastiest things that I had to do there were:

1-cleaning the public restroom (especially the men's room)
2- Cleaning out the chili and cheese pumps.
I will not eat anything from one of those to this day, disgusting.

Many people think you just stand around running the cash register, but that job can be hard work.

Stocking Shelves
Stocking the very cold walk-in cooler (although that was a nice escape from time to time)
Mopping up spilled Slurpee (constantly)

All in all, it was a very educational experience; it taught me how to deal with people, which now come in handy since I'm a teacher.