I usually try to take fresh items that are filling, like oranges, green/red peppers (cut up into strips), apples and low fat peanut butter (the protein helps as a filler), grapes (the water content in these makes them filling), fig bars, and other fruits and veggies when in season (i.e. strawberries, cherries, tomatoes, celery, etc.)
I also try to make bigger dinners when I do cook during the week, and then save the leftovers for lunch at school/work. Good items to save for lunch are chicken breast and steak (which can be eaten as is or cut up and put in a tortilla wrap with cheese and veggies – or steak can be cut into strips for a steak sandwich) & rice dishes.
I also occasionally take Lean Cuisine panini or flatbread sandwiches if I don’t have time to make something before hand. They have preservatives since they are microwaveable, but they taste fresh, have low calories/fat, and have a lot of different varieties.