You can also do "body weight" exercises.
The good thing is that even though they are very hard, you don't work up a huge sweat...(you can do these in the back room of a store quickly)
******Squat with an exercise ball.
lean up against a wall with the ball behind your back....feet 2 feet out in front of you...(so you are propped up against the ball)
Squat down until your thighs are horizontal. DO IT VERY SLOWLY UNTIL YOU CANNOT MOVE (about 1 minute or maybe 2)
Wobble back to your work...
******Pushups on a desk or other furnature.
Do push ups SLOWLY until you cannot do one...until you cannot move up at all....you push and push, but nothing happens.
******Dips between two chairs.
Use two chairs or two counters or two whatever to dip between...and as always...until total muscle failure....
The reason I say total muscle failure on each of these is that that's how muscles grow...by not being able to carry out the work required...they grow in response....
These are good exercises; these are "big" muscles that get worked...(more muscle = more fat burning)
I hope that helps...