What the best budget cooling option for a road trip in California - but only for one time use? I'll be weaning off the trip so won't need it again

So in Southern California , I imagine the temperatures will generally be between 28-32 degrees in a couple weeks when I go there. For part of my trip (over 7 days), I'll be travelling from LA and stopping off in various locations where I will have access to a fridge in my room - but not sure whether they will have freezer compartment...it's doubtful. Some places I'll be staying just the night, other places a couple of nights.

I was going to simply get the Frio Case which only needs cool water to activate...but at £19 it seems pricey for one time holiday use. With the price increase, I plan to wean off with my remaining pens so won't need to do this for another holiday.

I just need something that will last me for a full day before getting access to a fridge again.

I was also considering buying like a 150ml mini thermal flask and adding ice packs to it...but without access to a freezer, this may end up being useless.

Pretty annoying there doesn't seem to be a budget alternative to the Frio Case.