... open-toed sandals?
Saw an electrically heated, insulated travel mug at a "dollar" store and bought one. I didn't get it for travel use in my car; I got it for my computer desk and electronics bench. Now, no matter how long it takes to drink to the bottom, what's in there stays hot to the very end. I love this thing!
The supplied cord has an RCA plug on one end and a fused ciggie lighter plug on the other. The cord itself is way too stiff ... more like a weak spring ... and would be a PITA in any environment, so I put an RCA plug on some light-weight zip cord and connect the other end to either a bench supply or a wall wart, depending on which one happens to be handy. The heating element draws about 1.2A at 12vdc. I run it at lower voltage because 12v keeps coffee too hot for my taste.