So I gave a Hot dog Baron a joy ride in space. And in return, I was rewarded 320 tons of hot dogs. However, I can't seem to find anyone who's willing to buy hotdogs. What do I do with them?
A commodity is a type of cargo that the player can transport on his ship. Some commodities can be bought and sold at planets while others only appear in the context of a mission.
You need to go to a planet that also sells commodities or luxury goods. Those are the only types of planets where you will be able to sell it. It has no use otherwise (unless there is a mission that requires them.
Here is a write up about economies on planets: http://wiki.naev.org/wiki/Economy_and_Trade