how much jail time can someone get from littering?

You don't get jail time for that.  They put you on a chain gang and force you to cleanup litter along every highway in the WHOOOOOOLE country.  You can't go home until you're finished either.  If you miss a piece that's it....you're done.  They gon fry your lazy azz in the electric chair.

It is a misdemeanor in my state, which means up to a year in jail. I've never seen anyone sentenced to jail, but it is legally possible.

Unless you are caught DOZENS of times, jail time isn't even an option for littering.

I don't think any jail time, but you would be fined, or expected to pick up trash at work project, if you don't have the money to pay your fine.

The sentence for littering depends on what jurisdiction you're in. 

In most places littering is a misdemeanor subject to fine, but other areas may have different laws