Can a hot food container/thermos be carried on to a plane? I know it could not be if it had liquid in it like soup or coffee but what if it had solid food like chicken nuggets or fish sticks?
Yes. Why would you think this wouldn't be allowed? You can take a thermos with liquids on a plane, as long as you buy the liquids after you go through security.
You can always get a definitive answer to what is allowed by checking tsa.gov.