This is truck country, so know the law!
Most truck owners have been there, you or someone threw a can, a box, or something in the back of your truck, only to have the wind blow it out into other cars or the highway.
I'm certain someone could sue you or your insurance company if something blew out of your truck and damaged their vehicle, or even worse, caused them to wreck while attempting to dodge it (your little soda can could cause a whole "Final Destination" style chain of events that leads to mass casualties!)
Okay, enough with the hyperbole. In most cases, that piece of trash is just going to fly out and deposit it on or near our beloved Texas highways. Even though it "gives prisoners something to do", it's not cool and is definitely not legal.
So what's the punishment for having what the state of Texas calls "loose materials" in the back of your truck? Well, the fine is actually surprisingly light if you ask me. It looks like the fine is "not less than $25" and "not more than $500".
Here's something else for you to think about. "Loose Materials" don't just mean trash. If you're hauling a load of sand (it could happen), or even something like wood chips from your garden and it's sifting out through your tailgate, you are still violating the law. There is one exception and that's "agricultural product in its natural state" meaning if you were hauling a load of cotton or something, you're in the clear.