i have a no hot food policy (they don't want the place smelling when outside clients come in). i used to do leftovers when i had a microwave. now i do salad and sandwiches. i keep pantry salad items on hand at all time (chopped walnuts, craisins, almonds, feta cheese- ok its kept in the fridge but keeps for a while, dressings, roasted red peppers) and then buy greens each week with veggies and sometimes deli meat and cheese. i then chop up the veggies and in the morning can just toss together salad or sandwich. i also keep nuts at work to much on, yogurt in the fridge, string cheese, sometimes baby bell soft cheese wedges with crackers, fresh fruit, chips etc. i rotate the snacks each week as well. i also hard boil eggs, i can then toss in salads, eat for breakfast, or use for egg salad sandwiches. i sometimes make my own trail mix to munch on too, choc chips, cereal, mixed nuts and raisins.
sometimes if i have a pm shift i will do a grilled cheese type sandwich, rap in tinfoil and leave in my desk so its still warm when i eat lunch a few hours later.