lost a little black box
 

What is the little black plastic box behind the driver's side rear wheel? Has some hoses coming out of it. Important?

It's the charcoal canister for the emissions.

+1 to Rex. i dont know if it will kick the check engine light on, but it could. i dont think that MO does emission testing, so you might be ok. but i would look into getting it replaced. it has to do with the fuel tank and stuff.

It will definitely turn the SES light on. Most likely a P0455 will be set. You'll probably notice a fuel odor, but it won't affect engine performance, and you'll never notice a drop in fuel economy.

Ok. I did notice a little fuel odor since it appears to be a fuel line. I will look for a replacement online. Or can I just plug the hoses? The brackets that held it in place are rusted and have now been stripped ofd the truck due to a little off road adventure today.

The lines carry fuel vapor only, no liquid fuel. Until it's repaired correctly, you're likely to get EVAP DTC's.