Is there anything like the Rocky Mountain Tumbler cup, but bigger? It's ability to keep ice going throughout the day, even when left in sweltering hot cars with outside temps of 110+ is astounding to me.

I'm gonna be starting work soon and I'll be working in said temperature. I need something like that cup, but bigger, so it can last me through an 8 hour work day. Any recommendations? I don't know if just taking a standard 1 gallon jug and freezing it will work or if it'll just melt too fast or too slow throughout the day. I mean, I'll be getting lots of breaks, but I'm someone who cannot stand the heat. Even just being outside for a little sitting in a hot car, before I get the a/c on is torturous.