A walk from your den or hall that takes the time of the session to learn about the surroundings and some local history in close proximity.
Torch (if in winter months)
First Aid kit
Walk with a leader at the front and a leader at the back as not to lose any kids and have them numbered to 'sound off' periodically. A great idea to use walkie-talkies between front and back if your going to get spread out incase anything happens at the back so others can wait.