I would make a sandwich out of the light bread, like whole wheat Nature's Own brand and use mustard (won't spoil), deli turkey and perhaps low fat swiss or cheddar cheese and then bring a side of lettuce, tomato or anything that's like that to go on the sandwich and bring along some baked chips.
Also the pop off tops of tuna and five saltines.
If you don't have a fridge at work, you can use those freezer type things and put them in your carrier to keep your food chilled and bring some fruit salad and half a sandwich (perhaps tuna or egg salad.)
