Doubles as a sock dryer, sleeping bag/pocket warmer. The rigid model tastes fine for coffee, soft one is OK, but tea only. Opening is slightly smaller than the 1l size (touches my nose) but fits in pockets better. Others have described this system.
I use the 2 cup Ziploc (mentioned above) for hydrating oats/rice and will toss it in a jacket or sleeping bag, but it's seal isn't secure enough to do that when full of hot water. I met a thruhiker this weekend who soaks beans in them before cooking. I didn't ask if it leaks in his pack.
Tuck this combo inside a jacket, and I'm toasty. Good for making breakfast or lunch to-go in winter.