NATOPS requires flying gloves, id tags (dog tags), a pair of approved flying boots and any other personal equipment required by that T/M/S (type/model/series). Flying suits, socks, undergarments, etc. are not specifically required unless they’re in the squadron SOP.
A few aircrew have diverted to non destination airfields w/only the minimum required flight gear. Questions and charges usually followed for public indecency, though the charges were always beaten.