As for freezing water the night before I remember hearing that it isn't good to do this. Something about how the plastic in the bottle leaches into the water as it melts.
Anyway bringing outside food into the parks isn't a new phenomenon. It's been happening since at least the early 70s. I remember my mom and my brothers eating peanut butter and jelly sandwiches outside iasw from as far back as then.
Ok so I digress. Theres my contribution -- peanut butter and jelly sandwiches. Take two pieces of slice bread, white or wheat. Spread one slice with peanut butter. Spread the other with any jam or jelly you prefer. Combine the two slices. Put in a sandwich bag (or if you want to experience the early 70s again wrap in wax paper). Enjoy.