[ndt]

"The absence of ceramics meant that these foods could not be cooked – though roasting was an option. "

Actually people in some areas cook(ed) in tightly woven baskets with hot stones. As long as you keep the stones moving the basket does not burn. Additionally, you can use hollowed out wooden vessels or animal skins with the hot stone method.

[WildTurkey]

You can boil water in a paper cup.