How did ancient peoples boil water or cook rice before somebody figured out how to make metal pots?
Another way to ask this is: how would you cook rice if you found yourself stranded in the wilderness without a pot to cook with?
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You don't need to put a pot on the fire to boil water or make soup. You can put a clean stone in the fire and then put the very hot stone into the water in the pot. This way has been traditionally used in the Basque Country to boil milk to in a wood pot that would be quickly damaged if put in the fire. Basque language has even a word for those stones: esne-harri (literally "milk stone").
Furthermore, some traditional ways of cooking don't rely on putting a pot on fire but on putting it in an oven - a masonry oven that is just a chamber with thick walls that has been heated by burning a fire inside and after extinguishing it and removing charcoal and residues, remains hot enough to cook bread of to cook a dish (like rice) in a ceramic recipient, not necessarily suitable for direct fire.
if you have the option, make one out of clay as it's the most durable alternative.
If you don't, wood will do. Or if you're near a beach there may be large shells. The skull of a decent sized animal may also be available to you. If you're lucky enough to have a good sized piece of leather, some sinew, and an awl, you could make a water pouch with that.
Don't hang those alternatives to metal or pottery in fire of course as they can burn. But keeping them near some smouldering coals and embers can heat water pretty well.
More likely though you're not going to boil rice. You're going to turn it into rice flour, turn rice flour into a dough, and bake rice cakes out of that.