Save space and money by NOT buying and packing bottles of water! Each person should have a stainless steel or non-BPA plastic bottle - or at least reuse a purchased bottle of water and refill them from any sink or water fountain you pass. Water is everywhere! Take a sharpie marker and write each person's name on their bottle, or put a piece of colored paper around the label so each person's assigned bottle is easier to spot.
Trail mix for snacking with protein and fruit: granola, peanuts/almonds, raisins/craisins, dried fruit, plain Chex (any flavor), a few chocolate chips or M&Ms, seeds like pepitas and sunflower, etc. Put it in one big tub with a tight lid and a measuring cup or any plastic cup inside, then kids can scoop out what they want into their own container or a ziploc bag (which can be reused).
Take a small bottle of dish detergent with you - the smallest one you can find - and a small sponge or use the hotel washcloth. Take a few of your own utensils rather than relying on plastic, especially for preparation - a good knife or two for cutting fruit or spreading sandwiches, for example. Get a few extra towels (hand towel size is fine) to use as a dish towel or dish drainer. You can also use a clean towel as a "counter" for making sandwiches.
Most sandwiches can not only be pre made, they can be frozen. They defrost easily in a lunch box. PB&J, turkey & cheese, almond or cashew butter for those who don't eat peanuts, etc. Take meat for the first day, then PB&J for the others. Or stop at a supermarket deli and buy exactly the amount of meat you need. (We had a sandwich making "assembly line" for a function, and one very savvy mom asked the deli guy to give her 96 slices of turkey and 48 slices of cheese - so much smarter than estimating by the pound or half pound!)
Use the hotel fridge for yogurt or true perishables, not drinks. Kids can get free ice from the hotel ice maker. If you use your own bottles with wide mouths, ice and water go in great.
A breakfast of yogurt, some Grape Nuts sprinkled on top, and a side of fruit is great. Nuts provide healthy fats and help the kids not get a carb-rush from too much cereal or bread. If you take regular cereal, add raisins and nuts to it.
Prewash veggies/fruits and pre-peel carrots (larger carrots are way cheaper than the baby carrots, which are just peeled large carrots anyway). Hummus dip keeps fairly well even if it's not in super-cold temperatures.
I make a nice pasta salad with small pasta (I love pearl couscous which is also called Israeli couscous) or you could use rice, with added vegetables such as diced carrots, cukes, celery, grape tomatoes, green/red peppers,
rice vinegar and olive oil (or canola) plus salt, pepper, parsley flakes to taste. It keeps really well in a cooler, and there's no mayo to worry about. You can add beans or chickpeas for protein. Even the cucumbers don't get soggy for about 3 days, so it's a filling and nutritious salad. If you put it in a square plastic container with a lid, it fits better in a cooler than a round bowl. Take a couple of extra plastic containers with lids (stacked inside each other) for unexpected leftovers so you aren't throwing anything away.
The hotel fridge's tiny freezer will likely not refreeze your ice packs, so take some large ziploc bags you can fill with ice from the hotel ice maker.
Have fun!