Stretching and isometric exercises are best suited for a quick workout in an envoronment such as an office. You don't need to invest in any equipment for these types of exercises, just do stuff like pushups, toe-touching, jumping-jacks, twists and stuff. That will limber you up, and keep you in shape.

If you want to do more and you have the time (I envy you that if you do...) then check if there are any gyms in your vicinity.