It looks like a realistic tuna can that is found in a real-life shop. It comes in a circular green can with the food's name inscribed in purple text within a turquoise oval decorated by yellow and orange flowers.
Role in series
The can of tuna is mentioned by Mr. Krabs in the episode "Hooky" when he tells SpongeBob and Patrick they would either end up inside of one or be sent to a gift shop. Patrick ignores Mr. Krabs and continues to play with the hooks, resulting in a fisherman catching him and him ending up in a can of tuna at the end of the episode, asking for a can opener.