The trick is having a thermos. They sell really cute ones for kids at Target. (Bakugan, Star Wars, Hanna Montana,etc.) I've found that a lot of stress on "what to pack" got reduced when we finally got them thermoses. If I make spaghetti 1 night, they have it for leftovers the next day. If I make tacos for dinner, they have nachos (with the left over taco meat) or I stick a tortilla in the lunch box, with the meat, and shredded cheese and they make themselves a taco. Chicken nugs & chili are great in there.
One of my sons likes pasta salad, the other does not, but that is another idea, thermos not needed for that, just an ice pack. Do they like cold chicken? Will they eat a drumstick cold? Leftover pizza if they will eat it cold.