Umm.... I used to freeze bottles of water too... but now "they" are saying that freezing or heating ( like microwaveable bowls) plastic releases toxins that cause cancer. I dunno how true it is... but I have seen that 90% of the microwavable/frozen food bowls have been pulled over grocery shelves in the last year or so.
Yup, just go with a knapsack or fanny pack. Ask Santa for the English saddle trail pack.
"There ain't no vaccine for stupidity* Maxine