Lots of choices, a little of everything seems to work. If you can, get your kids involved in preparing/helping, even if it's on the weekend. I just listened to a program about childhood obesity rates going down as more people cook and get involved in what they're eating, rather than grabbing the 100 calorie processed food snacks and the Capri Sun/juice box things.
Kids like to dip - so hummus or a healthy ranch dressing and different raw or lightly-cooked-and-quick-cooled veggies: carrots, celery, cucumber spears or disks, zucchini spears, broccoli florets, cauliflower florets, jicama sticks, even slices of fennel bulb, radishes, pepper strips. Fruit cubes - for fun, thread them on a long toothpick (I like the cocktail type with the little arrow head on the end because the fruit does't slide off, and they can even be brought home and rinsed and used over again): cubes of cantaloupe and honeydew, watermelon, kiwi, apple or pear (spritz with a little lime or lemon juice to prevent browning), grapes, pineapple, berries. Mix them up like little shish kabobs with alternating colors. Kids can have fun making their own the afternoon before. Just put the fruit chunks out in piles on the cutting board or maybe in little bowls, and let them create their own "kabobs".
Get one of those divided lunch containers with little compartments, and load them up with a little of everything.
In addition to sandwiches, you can try French toast sticks with a little powdered sugar - I make it with soy protein powder and a lot of cinnamon with the egg, and the dark cinnamon helps disguise the fact that I use whole wheat bread. Skip the syrup because it's messy - unless you use real syrup which only requires a dab (the other is almost all high fructose corn syrup).
Hard boiled egg disks (cut with an egg slicer but "reassemble" it and it fits perfectly in one of the compartments.
Sticks or squares of low fat cheddar cheese. Laughing Cow spreadable cheese (much better than any Cheez Whiz type of product) on regular Triscuits (just whole wheat and a little salt and canola oil, vs. Wheat Things which have high fructose corn syrup). Or put a little turkey or peanut butter or almond butter on the crackers - just as good as a sandwich, but kids think it's snack-y. Same goes for rice cakes.
Wraps - a slice of thin turkey, thin sliced cheese, a leaf of romaine lettuce or a few spinach leaf if you can swing it, spread with a little hummus - roll, secure with toothpicks and cut in sections. Or make a Mexican wrap with a corn tortilla, spread with vegetarian refried beans, and add whatever they'll eat: chicken, other beans, cheddar or Mexican style cheese, some green peppers. Roll like a wrap, or fold 1/3 over, roll once, fold in the 2 sides, and then the final flap, and secure with toothpick. If they make their own, you'll have an easier sell.
A small container of almonds - great protein and crunchy. Use whole roasted ones, slivered, whatever they will eat. They don't have to be salted.
To drink: WATER!! Ideally in a reusable stainless steel bottle. Schools are going crazy hauling plastic water bottles in the trash. And it's just not necessary when tap water (better regulated than bottled water) is free.
I think it's great that you are looking for healthy solutions! A friend who is a kindergarten teacher just goes crazy when she has to deal with kids who have lunches full of white starch and sugar - the kids are off the wall after lunch and then crashing a half hour later. The kids from many other countries have much better snacks (e.g. kids from Indian families and many from Latin America have much more fruit/veggies and virtually no pre-packaged stuff).