Between 1977 and 1984 I wore no other socks in warm weather, and had about 20 pair of them. Each lasted about 20 wearings, then they'd blow out at the heel and I'd get new ones. They're light, thin cotton (97%) and now have some nylon for anti-blowout properties, and for hot weather riding in sandals, it's good to keep the sun off your thin foot skin. Cheap thin classics, made since 1922 or so. They'll sort of stay up, but push them down.

Two pair per pack, with instructions for making monkey or elephant dolls.

Get the Medium if you wear up to 9 men's shoe size. 
Large for those who wear up to men's size 11.  
XL for up to men's size 13.