During VBS the kids each got a drawstring backpack. I have turned them into daypacks for hiking. They contain snacks, water, a small first aid kit, a small flashlight, a small bottle of hand sanitizer, a bandana, kid binoculars, and a five in one emergency whistle, (whistle, emergency mirror, compass, firestarter, and container for matches).
Having daypacks makes even short hikes seem like an adventure and they carry their own stuff. The key is to have useful items, keep it lightweight, and no snacks that will melt.