What, no pesto pasta! No bread either.... that IS hard work. Be aware of this article: www.bbc.co.uk/news/health-49448945
We have quite a bit of "kit" to keep things hot or cold. I recommend what Thermos call an "ice board" and a good insulated sandwich bag. We often leave half the food in a proper coolbox in the car if it is a long day. DD tends to graze her way through galas so I make sure she has plenty of snacks in little pots.
Houmous and carrot sticks is a favourite and I'll tend to throw in a few cherry tomatoes too. Babybels/sticks of cheese or cream cheese and breadsticks are easy to pick at.
Pop corn and the trail mixes by Graze are popular too (just watch out for the nut policy wherever you are). I'll sometimes buy some fresh coconut, otherwise I make up some pots of fruit fresh (apple/grape/pomegranate) or a semi-dry mix of apricot/apple/pineapple etc.
I did try frittata-style muffins, but they were vile (think it was the recipe I used), but I do sometimes buy mini omelettes (Unearthed make them) . DD also loves scotch eggs, but they are most definitely kept away from poolside because of the smell! Those picnic eggs can go poolside.
We also buy those pouches of grain/pulse mixes and use those as a base of a salad (Merchant Gourmet and Jamie Oliver do some). Throw in some chopped tomato and a cheese like feta, cubes of diced roasted sweet potato/butternut squash/beetroot etc with a bit of dressing.
DD often has thick chunky soup to which I add a bit more chicken (the sort of thing they sell in the chiller aisle). If you put it in the thermos bowl almost boiling it will keep warm. Or maybe chilli and couscous.
Some of her friends have baked sweet potatoes.
Banana and chia seed muffins are quite filling if you find a recipe with wholemeal flour (I probably throw chia seeds into a lot of her milkshakes/smoothies etc.). Then there are flapjacks.....
Good luck this weekend.