We did this in December for the 48HFP International Shootout - theme was "End of the World" and there weren't any other required elements.
This was our 12th film in timed competition, and one of the most difficult. The story & idea just didn't come together early on so we just winged it when we shot. The actors were all miked wirelessly and then we just turned them loose to improvise for most of it.
We shot on two 5DmkII with various lenses - definitely a challenge to cover 4-5 people improvising at one time with those cameras. Pulled a lot of the story together in editing - I leaned heavily on the music, great stuff from an artist called brokenkites (hollowscene.com). It came right down to the wire so the color correction was pretty rushed, but somehow it actually came together into a film.