Yes, olive oil.  No, I'm not kidding!

Unrefined olive & coconut oils, and shea butter, have a natural sun protection equivalent to about SPF 4-6.  That means if you are super pale and can't stay out more than 15 min w/o burning, extra virgin olive oil will give you an hour.  For most folks, most of the year, olive oil will get you 2-4hrs protection all by itself.

I've tried it.  It works.  With no chemicals, and the added bonus of being a wonderful moisturizer!  Affordable, too. (esp. compared to commercial natural sunscreens)

Caveat: do read my experience with using it over the course of a day in FL here.  I've found that re-applying will only get additional sun protection if preceeded by a good long session in the shade first.

(No, it's not greasy - just use a little, and it rubs right in.)
(No, it doesn't fry you.  Chances are, the "oil" you remember your friends coating themselves with in the 70s was "baby oil" (mineral oil, a petroleum product), which, according to one site (which I have NOT substantiated), dissolves the skin's natural oils, leaving you more exposed than if you had nothing at all!)
(We keep it in an old vitamin E oil container - holds an ounce or two - with a flip-top lid reclaimed from a lotion bottle.  Perfect, and lovely, too, with the golden oil & black lid.  Fits perfectly in my purse or glove box.)