Stop and go city driving will definately be better with less weight - remove the rear seat if you can - the plastic interior is not really a lot of weight to worry about. Put some better gear oil in the tranny if you got a manual and that is good for almost 4-5 mpg alone. More tire pressure (40-42psi) is good for a few more MPG as well but it will ride harder and will not mean much in stop and go driving only highway. The big fuel eater with stop and go is the weight. To get the best mileage use quick acceleration and then drop it in 5th and back off the gas and coast - what is know and pulse and glide or just putt putt in 5th without any gas if you can drive at a steady slow speed.