The Chaturanga Push Up - this exercise alone incorporates hamstring flexibility, core and upper body strength. They can be performed often and I highly recommend office workers to get away from their desk a couple times a day to do these.
Chaturanga Push Ups x10 (Modification: use knees)
50 jumping jacks
1:00 plank hold
30 second side plank hold/side
Reapeat 3x