Hi J.,
YOU know your child's tastes best, so begin by making a list of the foods he likes and will eat. Remember, you can always send along a container that keeps food hot/warm filled with soup, stew, baked chicken nuggets or casseroles inside if you want him to have "hot" meals. Thermos makes a great one, called the FUNtainer, that keeps foods hot OR cold for about 6-7 hours in lots of kid designs, in wide-mouth versions he can eat out of. They sell online and in stores for about $15 or $16, but are incredibly worth the money:
http://www.thermos.com/product_catalog.aspx?CatCode=LUNC
My food suggestions would be cheese cut into sticks or slices, sliced meats like turkey and ham, whole wheat crackers or breads (there's oodles to try) sliced in half. He could make his own sandwiches or cracker stacks, and you can make them healthier than Lunchables ; ) You could also pack fruit you've sliced with some yogurt or low-fat caramel dip in a small cup, or this easy recipe for Rocco DiSpirito's Jammin' Jelly Dip:
Simply mix together:
1 cup low-fat cream cheese, softened AND
1 cup sugar-free jelly, strawberry or your flavor of choice
Does he like pizza? Have him help you make his own on English muffins with some sauce, cheese and whatever else he likes, heat til the cheese is melted, and place in a sandwich container and send. If it gets cold it's OK, kids seem to love cold pizza. Do an internet search for kids recipes, lots of big name chefs have families, too, and have cookbooks out and recipes online.
If he'll eat cut-up veggies send some with a dip like this recipe for Rocco DiSpirito's Tomato Ranch Dip (I figured out that the tomato "puree" listed in the ingredients is tomato "sauce") :
http://www.rachaelrayshow.com/food/recipes/roccos-tomato-...
BTW, I've made both of these dip recipes and kids & grown-ups alike love them : )
To drink I give my little guy (he's 2) the juices that are 100% juice and have a full serving of fruit and vegetables in them, since he's picky about textures when eating. They're good for him, I've found them in juice boxes, and he loves them!
To take it all to school here's a bag I've seen advertised that I want to try, the Pack-It, a personal cooler, so to speak, that is non-toxic gel-lined inside and you keep in the freezer when not in use. It is advertised to keep food fridge cold for 10 hours, but most reviews give it more til lunchtime, which would work for your son. I haven't seen it in stores as of yet, so here's a link to a page listing sites where it can be ordered (some do offer free shipping depending on the size of your order) :
http://www.google.com/search?q=pack-it+cooler&hl=en&a...
I hope some of these ideas help, and am glad you asked the question because it got me thinking ahead, too!