Non-nudists Stranded in a nudist resort, or on some kind of nudist island, would add some tension - would give it a bit of backbone.
Extra tension if it's several people stuck that wouldn't necessarily (like to) see each other naked normally.
Family certainly works for this if you like the incest or incest-lite-embarassment angle.
But if you don't like the incest angle, it could also be co-workers (maybe with a hot boss lady).
Or - students on vastly different rungs of the social ladder (nerd and cheerleader, or geek girl and jock, or nerdy boy and jock, or groups of the above, or nice girl and bad boy, or bad girl and nice boy, or one geek and tons of cheerleaders, or closet lesbian and... - you get the picture).