Girl briefs. Guy briefs. Whatever covers my butt, doesn't ride up, and is (regrettably, due to the first two factors) totally unsexy for either gender, because of how little I like to spend on them. If I'm not packing, nobody's going to see the things anyways, and I have more girl ones than guy ones, so may as well wear those ones if I don't need the extra space.
I don't know how anyone still retaining girl parts can wear boxers. They just don't stay down, and it seems as though one reason behind the euphemism "snatch" is because that's exactly what those parts do with any extra loose fabric, of which there is plenty where boxers are concerned. Pain. Pain. Pain.
Could never get used to tampons. Tried a mooncup once. Just...no. Think I'll save it for if I ever go camping - might need it for a snakebite kit. That kind of bleeding just gets treated like any other sort of wound.