I'd say the number one item would be a canteen. I've been working with kids a long time, and nothing kills the fun like a little dehydration headache. Knives and fire if you think they are responsible enough, otherwise there is no harm in making those an "only when Dad's around" thing.
Big orange trashbag for signaling and shelter is a great idea too, a 9 year old can get pretty lost not far from camp if they get geographically mis-placed, and anything that makes the finding easier makes for a better time for everyone.
flashlights are good, glowsticks are cheap as well, and a good night signal if a fire is a no-go.
As for the fun stuff toys like binocs and magnifying glass, those are great! there is a lot to be learned out in the woods, and the more he can learn, and explore the more he'll want to be out there, than inside in front of the TV later in life.
Even if he wanders around with a small backpack filled with stuff, if it's his stuff, and its cool stuff (half the forest of twigs, leaves and bugs!) he should be having fun. you might have to carry it on the way home, but those are lifetime memories. My dad had to start putting limits on my rock collecting, or he would have been able to re-gravel the driveway with the rocks I asked him to carry for me once my pockets got full!