I have the same problem! Sometimes I solve it by making extra salad with the night before's dinner. Then I put it in a container for the next day. I find that if I put everything but the lettuce in, then the dressing and then the lettuce on top, the acidic dressing doesn't destroy the lettuce. Sometimes if I don't have a salad in the dinner, I find other parts of dinner and make it into a salad. I made fajitas the other night and I chopped up extra avocado, cheddar and tomatoes and had that with salad dressing the next day.
I also buy those little low-fat string cheese or cheese slice package things and bring those with me.
Oh! And a smoothie! I make a smoothie in a thermos and drink it at lunch - bananas, berries, low-fat plain yogurt, ice - all in the blender and then into the thermos. Very filling. My roommate likes it with vanilla yogurt but I think it is too sweet that way.
Make your own trail mix too - I use mixed nuts (unsalted) and dried fruit - cranberries!
An apple with a few slices of cheddar is great too. I always try to get some protein in there (cheese, nuts, thinly sliced meat) so that I don't get hungry again too soon.
