Maybe calling it a kit might pushing it, but my boys loved having these little books for their treasures they found hiking.
We also brought along a jar for bugs and a cheap-o magnifying glass for close inspection.
These books can be super fancy or basic like this one. I just used 4 Ziploc bags and taped them inside some construction paper.
Each page got a sticky label with the name and a drawing of the item to be collected on it.
That's about it. It's a nice way to keep the sticks, rocks, leaves, etc. that your child collects on a walk all in one place and not filling everyone's hands.