I'd add in the crew, a few US soldiers riding on the back would be cool as well. The farmer idea is a good one, you're gonna have to reposition the driver's head though. Finally I would add in grass being pushed over by the vehicle, right now the path looks way too "clean." Good luck with the project, it looks good so far.
EDIT* The cowboy hat is a really nice touch, however it is far too open, a gust of wind could carry it away. I like it in the diorama, but I'd put it on the inside of the crew compartment. Maybe adding in a few bottles of wine or bread from nearby houses would look good as well.