We got a cooler backpack from Target for $25 this summer and used it in the parks. Plenty of room for 3 o 4 water bottles. Mesh pockets on each side to carry water bottles. the lid has a zipper compartment big enough to carry a few snacks. A nice size zipper area in the front for phone, napkins, poncho's. Plus a mesh pocket in the front as well.
I carried frozen water and the water stayed cold all day in the HOT summer temps. We took it to the pools.
Also good if you get a meal and don't finish it you can bring the leftovers back to your room. Just ask for a large cup of ice to place in the bag with the food. I did this with a meal I got at the Rainforest at the AK.
http://www.target.com/p/igloo-maxcold-maxpack-cooler-black-w-gray/-/A-15373015