Some brief searching ("cooking rice with seawater") indicates that at a minimum you can use seawater diluted with fresh water for cooking if your survival depends on it. Seawater is around 3.5% salt. For perspective, that is something on the order of a soup spoon of salt per soda can volume of water (12fl oz/355mL).

Undiluted seawater suitability seems to vary by food[1][2], my cursory search didn't provide any factual specifics for rice, oatmeal, and vegetables. Some comments indicate you can boil fish in straight seawater.

That's all without considering pollution and natural toxins from algae blooms. The sources I skimmed mentioned commercially sourced culinary "sea water", I would expect some amount of filtering and heat treatment.

[1]https://www.chowhound.com/post/cooking-seawater-785862

[2]https://www.quora.com/Could-seawater-be-used-for-cooking-e-g...

https://cooking.stackexchange.com/questions/51729/can-i-use-...

Not in sea water, it’d be far too salty to be edible. You’d end up drinking more water to compensate.

I understand that pasta cooked in seawater is passable as most of the water (and salt) is discarded. Normally rice absorbs all the water, I don't know if you were clever and boiled it in lots then drained it if that would work.

Would take a lot of fuel though, usually propane for the USA, I think? In the UK many use Butane instead, or CampingGaz - in any case you don't really want to use it all up when you are out at sea.

No, because all of the water ends up incorporated in the rice. Try making rice where you add 1 1/2 tsp of salt to each cup of water

I wonder if you could use dry rice to soak up salt

Not if you want to live very long.