At 18 I'd say try anything, you've got a clean slate, and there's no reason why you should restrict yourself in any way, other than avoiding things that you feel are morally wrong, or that will expose you too much to things you may be sensitive towards.
Retail is a good way to go, though seems to be a career on the wane with so much online shopping.
One on one interaction isn't as overwhelming as it seems once you settle into it, and you can spend time familiarising yourself with stock and the layout of the store, which will be easier for you to remember once familiar than for some others.
It's also not a bad idea to register with an employment agency; one of the ones that can send you out for temp positions, whether in admin or industrial work; that way you can try a wide variety of things before you decide what you'd like to do longer term.