What do you put by someone's gravestone?

I am talking about a grave at a veteran's cemetery. All of the headstones are close together. This is for someone who died a few years ago. I am not going because of an anniversary or anything, I am going just because. I know people put flowers and flags, but what else do they put there? What kind of flowers do they put? Do they put pictures? What about personal items? What happens to the stuff that isn't biodegradable?