My first summer job was at "Italian Delight," a mall pizzeria that was located near my house. The place was largely staffed with Latin American immigrants of questionable legality, with the occasional high school student thrown in for good measure. Although I only worked there for a few months, I learned three important things that have stood me in good stead for the rest of my life:
Knowing how to swear in Spanish is a worthwhile skill. It has paid off far more than most of the junk (like Algebra II) that I was learning in school at the time.
Don't order sausage rolls. One of my first jobs at Italian Delight was tearing the sausage strips out of old rolls and putting it into new rolls. Seriously. It quickly occurred to me that the sausage could, conceivably, be reused indefinitely. I permanently stopped eating sausage rolls.
Bleach cleans anything. It will even clean skin, although the skin will then tend to fall off.
The third thing ended up being the most useful, as many of my subsequent jobs in the food service industry involved cleaning of one sort or another. In fact, looking back, the most important thing that I learned at Italian Delight was the vital importance of obsessive cleanliness, a lesson that was drilled in at Jerry's Subs and Pizza, McDonald's, and Bollo's Bakery and Cafe.
Unfortunately, however, my experience seems to be somewhat atypical. While my bosses were borderline paranoid about killing germs, cleaning floors, scrubbing surfaces, and ridding the world of grease, many restaurants don't seem to have the same scruples. In fact, a recent article noted that, on average, restaurants in Tennessee received an 82 out of 100 points on their health inspections. Only a third of all restaurants scored 90 or higher. Worse yet, these restaurants are only inspected twice a year; granted, these are unannounced, random tests, but it would still be nice if they happened more often!