1. Do a squat every time you pick something up. Instead of bending over in the usual way, which stresses the lower back, bend your knees and squat. This forces you to use your leg muscles and will build strength.
2. Every time you stop at a traffic light (or the bus does), tighten your thighs and butt muscles and release as many times as you can. (Don't worry, no one will see it!) This will firm leg and buttock muscles, improve blood flow -- and keep you mildly amused!
3. Whenever you're standing on a line, lift one foot a half-inch off the ground. The extra stress on your opposite foot, ankle, calf and thigh, plus your buttocks, will help firm and tone muscles. Switch feet every few minutes.