I tend to snack throughout the day instead of eating meals when I'm at work. My favourites:
-can of tuna! -- not everyone likes this, but I think it's yummy. Just make sure it's a brand that isn't packed with oil/salt.
-salads! I know that this might sound gross, but I like to eat them as finger-food. This makes the whole salad last longer, and makes it feel more like "fun" food.

-if your plan allows, bananas are good and filling, and high in potassium.
-if you're careful to mind the sodium, pickles are great; there are some great low-cal pickles out there...yum!