It never occurred to me to ask one of the vendors for a cup of ice. That's brilliant, and no I'm not being sarcastic!
We went to Disney several years ago. We ate breakfast before we left for the day. We brought sandwiches, drinks, chips and fruit in a back pack. We just kind of accepted the fact that our drinks would be warm. We ate dinner out each day. By that time of day, it was nice to have someone else prepare the meal.
It gets so busy at the parks and the lines are so long that it was actually really nice to be walking somewhere and just decide to stop and eat a sandwich. We were with the extended family, so it was actually really nice to be able to do that since we were with a very indecisive family. (Can you tell they are my in-laws?)
I carried the backpack all day, and I really wasn't bothered too much by the weight. Just the one kid at the time, but he was in diapers!
If it were me with older kids, I would pack drinks, sandwiches, fruit, chips and a packet of baby wipes. I think I will be buying baby wipes for the rest of my life. They just really come in handy!
Have fun!