What about in tupperware containers? I had to take a bus trip and bought some cheapish tupperware and smashed holes in the tops for air and was able to keep them warm by having them in my lap :c
I think the gatorade thing might be okay, I think I know the bottle you mean.. Make sure its crrazzyyy clean, though, of course. You wont be able to keep it closed all the time, though- remember that! Maybe, if you can, get 4 caps, 2 unholed and 2 with a hole or two, so when youre able to just have them, you can allow them easy access to air from the holes.
You can also bag them and keep them again in a single, larger tupperware container, with seperate baggies of course- and put like a paper towel in between the bags so they dont see eachother. Again, make sure the bags are opened once in a while to allow air in. They can be kept warm in your lap- I took a long car trip with no heat (BRRRR! D:) and managed to keep my two boys (in their cups, about 1.5 in of water) at a balmy 76-78' with just my...er..lap warmth! XD