Wilderness Advanced First Aid training always looks good to Park services I think. Also if there's any sort of volunteer rural search and rescue squad in your area? If you join up they will occasionally fund classes on things like tracking, survival skills, navigation, etc. focused on wilderness, and they would already likely be working with any large protected parks in your area from time to time when someone gets lost in the woods, etc. My buddy was a physics major who worked (I think) laser optical measurements in school so I think it was mostly his extra-curriclars that led him to the job anyway. He did a lot of hiking and climbing. Next time I talk to him I'll ask him how he found/got the job though!