At the moment, mine looks like this...
10 reps of the following:
Standing leg swings (each side - dynamic hamstring stretch)
Split squats (each side - dynamic hip flexor stretch)
Standing leg swings
Takes about 3-4 mins which IMO is enough to get the heart-rate going, and I think it covers all muscle groups whilst addressing shoulder/hamstring flexibility (which I'm sorely lacking).
My best Fran is well under 3 minutes rx'd, but a full Crossfit warm-up I'm convinced would take far too much out of me. Never done one though, so it's just speculation.