Let's face it, modern humans survived for 200,000 years with no other toys than these. And what did that get us? Everything great, as long was we ignore rampant global warming, war, terrorism, and over-played pop songs. So given the results, I have to say, the humble natural toy has stood up pretty damned well.
Consider the stick. Every boy knows that the stick is a gun and a sword, at the same time. I shot more indians, back robbers, enemies, and friends with those stick than I can count. Sticks are free. You find them littering the ground. They are destructible, meaning that no adult will ever yell at you for destroying one. They burn, which means poking them into the fire and burning them down to the nubs. Even better, you can break up all the sticks to make the fire in the first place. Can you get cooler than that? Not only that, but you could swing them around dangerously.
The ultimate form of the stick is the tree. If there's a tree that can be climbed, it will be climbed, even if you have to nail old boards to it. The purpose of trees is to be climbed, and otherwise provide sticks and leaves. There was really no ultimate point in climbing trees, it was just one of those things that had to be done.
As for rocks, these gave us boys our first access to truly hazardous weapons. Forget putting an eye out, you could cause pain at range. Rocks were so hazardous that your ass was grass if you parent caught you throwing rocks at each other. (Never mind that centuries of boys have the bruises to show for this. Parents have to put on the show even while knowing that the boys are assaulting each other. Your job is to keep it from getting out of hand.) Flat rocks could be skipped across ponds. Not-flat rocks could be hurled at whatever other objects were available (preferably glass ones that broke and not wasp-filled ones that caused you to run in terror.)
As for leaves, their uses were just as myriad. Their most famous use is as a leaf pile in autumn. If there's a pile of leaves being made anywhere near children, dollars to donuts, those children will destroy that leaf pile by hurling themselves into it. When my daughter was tiny, her first response on seeing such a pile was to climb it, then bury herself in them. She needed no instruction whatsoever. Leaf piles rock.
Leaves themselves are the ultimately available bendy-material. If you were playing with toys and you needed something flat and bendy, leaves were it. Leaves always part of my stick-buildings so that the top dirt layer would not sift down between the sticks of the roof. My daughter uses leaves and grass to make dresses for her fairies. Where there is fire, there are inevitably leaves to get burned in the fire.
As for dirt, where would we be without dirt in all its forms, from dirt piles to mud pies? I are say that ate certain ages, as boys we would voluntarily spend more time in dirt than in any other condition. It's as if were were all wild boars, needing that coating of dirt to keep the insects off our backs. Meanwhile, our mothers were fighting the good fight to keep us clean. Eventually this escalates, especially for those boys with powered off-road vehicles. It's about that time that mothers give up, and boys think that all that dirt is great until girls start looking a whole more touchable than they did before.
An important part of dirt is trucks. Trucks doesn't just mean trucks, it means any vehicle of bigger size appropriate to playing in dirt (bearing in mind that a boy's definition of appropriate doesn't match anyone else's definition.) Almost always, these sorts of toys are earthmovers of various sorts, but with leeway, a firetruck or ambulance can get slipped in. Work areas always proved suddenly hazardous, especially if dinosaurs showed up. (This has been known to happen.)
I don't think that boys ever get dirt out of their souls. Grown men dominate the construction and mining industries, and if you want the ultimate in dirt-toys, those powered behemoths called earth-movers shame everything else.