When I see "Texas" I think HOT! . . . so I don't know if these things will work for you. We're from outside Philadelphia & in the summer it does get hot here & I use them then.
First, when it's hot I always freeze their juice box to keep things extra cold. DD complains that it doesn't always melt, though, so I started giving her a plastic spoon. Then she can open the box & "eat" it like a slushy.
Second, all year round I do put in one of the frozen blue things, but I guess you already do that. Anyway, their lunches are usually kept cold enough to give them:
egg or tuna salad on pita
hoagie - I think it's the lack of mayo, but for some reason I think of these as "keeping" better in the heat
chicken salad (the kind w/mayo)
grilled chicken on a lettuce salad
DD's favorite (her idea, not mine

) "lettuce, mayo, pickle & cheese"
cold, left-over pizza or stromboli
meatloaf sandwich (usually w/ketchup not mayo)
sliced baked ham on a roll
ham salad
yogurt
2 hard boiled or red-beet (pickled) eggs with a side of pasta salad
Pepperoni pasta salad (has mozzarella, pepperoni & veggies)
I have to admit, I'm always glad when they want to buy. Coming up with different stuff for lunches gets to be a drag.
Deb