headlight bolt came out

i'm in the middle of nowhere on a 4 hr drive, 1 1/2 hrs drive from nearest help at 12am and my headlight starts bobbing up and down a little, i figurd i'd stop in the next small town where there might be some street lights to check it out, then hit a bump and bang the bolt on the "hinge" part of the light dissappears and the headlight's loose... i get to drive the next couple of hours on one headlight, at a somewhat reduced speed.
i don't know the size of the bolt or where to get one round here, so it's probably gonna have to do me for the first couple of hours of dark on the drive back home 4am tomorrow morning... fortunately i should be on good roads till it gets light, unlike last night when i was stuck on bad roads in the dark.