Can a DNR officer take your stuff?

yes if it is stolen or if it is illegal

Added: In most(all?) states DNR (Department of Natural Resources) Officers (i.e.: Game Wardens - Rangers - etc) are sworn law enforcement officers who possess all the powers of the "regular" police and there would have to be a legal reason for their confiscation of your property. Considering their realm of specialized activity this most often takes the form of confiscating firearms, Archery equipment, and fishing tackle (and anything else) used in illegal hunting and fishing activities.