I keep three lunch ingredients at work: bread, peanut butter, and jelly. I eat that most days. Occasionally I'll bring a deli meat sandwich or leftovers from home.
I usually bring a banana, apple, crackers or something with me to snack on during the day. I tend to snack a lot in the mornings, especially if I woke up early and went for a run before the commute (about 3x per week).