One thing, though, is that it requires a lot of oils that many of us can't use. Might be able to find something to substitute with, though.
However, in the interests of the most natural sunscreen ever, I remind you of pigs. Who roll in the mud not only to keep cool, but as a kind of protection from the sun, too.
That's right: rub mud on your skin - the most basic form of sunscreen there is.
Now, that sounds silly for folks who are going to, say, an amusement park or a picnic. Most of them dressed up and don't care to have mud all over. However, if you were, say, hiking, or gardening? You have a hat on for face protection, so typically you just need arms and legs. Which are going to be getting covered in dirt anyway, so hey, why not just rub them down with a little wet dirt and save the money on sunscreen? Or the possibility of a reaction, at least if you can find some clean dirt that's not, you know, contaminated by heavy metals or something.
I have a friend whose grandmother used to do this when out gardening, living out west and not having sunscreen at the time. Everything old is new again, I guess!