I did some poking around on the net. Seems like most cemeteries don’t allow any food or drink. However, since you were saying that this cemetery has a lot of regular passers-by, and is setup more like a park, it may be thought of differently. Still is kinda odd, though. As long as those people know why the hotdog cart is there and what they are honoring, I think it’s ok. Hope people don’t throw trash off the side of the hay cart. I’d probably pick it up and throw it back at them.
This was all very controlled. I didn't see any trash. The Boy Scouts place flags on the military graves and they have a wonderful memorial service every year. It really is quite a nice and respectful experience. I just never thought about a hayride and hotdogs in a cemetary on such a solemn day.