With kids, bring action figures or Barbie’s and use the natural materials to build forts or bridges or cabins to furnish or things like that - but bring a blanket for you to lay on and actually play WITH them. It gives Mom some time to relax, read, or whatever, and you get to see how your kids play imagination games. I’ve had a blast putting Barbie’s through Survivor competitions, or making log cabins, or when the toys “explore” and collect shiny rocks.
It gives them something familiar to do that I guarantee they’ll remember doing with you, and it had YOU doing THEIR thing some, which for most kids is a nice change.
We’ve also done zip lines, made stick weapons to hunt bad guys, done geocaching, (natural) art projects for other people to find, carved things (they love that), and of course had campfire stories (not ghost stories, ours always involve silly aliens, planets made of things like cheese, huge animal companions, etc)