Yep, after purchase is my usual time to remember
I also have a temp control solution for my trunk, it's a tote that keeps cool things cool and warm things warm. I use it so my frozen groceries don't melt - I too live in a very warm climate.
I haven't used it for my Kindle yet, but expect it would be good for that too. They have it on QVC now, if you search "expandable cooler tote" or item F06868.