Dear S.,
First, there aren't enough words thank you to your entire family for the sacrifices you are making so your husband can serve the country... Bless your family, and many prayers that he gets home safe and well when his tour of duty of done. Second, welcome to Fort Lauderdale!
You will find hundreds of healthy snack choices at Whole Foods Market. It's on N. Federal Hwy. (US 1) in Fort Lauderdale. There's a bigger one a few miles north in Boca Raton, just as you turn East on the Glades Rd. ext.
You could buy big bags of snacks then put them in baggies for your son, or choose from lots of pre-packaged mini snack sized packets of healthy crackers and other snacks. Such as mini peanut butter filled crackers (if no peanut allergy...), real fruit cookie bars, pre-made granola or make your own special trail mix, and there are mini packs of non-perishable milks (chocolate and plain) and soy milks. You could freeze them before putting them in his lunch box, even if they aren't ice-cold after school they still won't go bad. The carry fruit "roll ups" that are all fruit, no corn syrup. Mini applesauce cups also. You could make mini peanut butter & jelly sandwiches for after school, if he's like my youngest son, they love the crust removed.
I've been shopping at Whole Foods here (and in Calif.) since before my kids were born, 2 boys ages 8 and 10. They and their dad all get "shaky" with low blood sugar if they don't eat every 3-4 hours... so I hear you about your son. And it's great that you figured out it's because he needs to eat, rather than just blaming him for being "cranky"!
WIshing you all the best, and if you have any questions about Fort Lauderdale, feel free to contact me, I'll answer anything I can.
~ C. N.