Make sure your tyre pressures are as recommended. Over inflating might save you half a litre of fuel every 100 km's, but you'll end up replacing the tyres far sooner, so keep them at the manufacturers recommended pressure.
Weight savings, by removing things, are possible, but the amount you save on fuel, for instance by removing the radio, would be far outweighed by the sheer boredom of driving with no choons!
You could always walk more. That way you save the fuel of the journey, and over time you'll lose weight from all the exercise, and so when you DO drive you'll use less fuel too.
But in all seriousness, the standard advice to save fuel is to drive smoothly. Accelerate away smoothly, brake as little as possible by planning in advance, slowing down using engine braking. If you're going down a hill leave the clutch engaged. Modern engines will sense that the engine is being turned over by the momentum of the car and will stop fuelling. If you "coast" down a hill with the clutch disengaged/the vehicle out of gear then the engine has to use fuel to keep itself turning over.
Keep the windows closed. At any sort of speed, an open window can add 10% to your fuel consumption. Also avoid the use of air-con unless absolutely necessary.
There are loads of things you can do to improve economy, most of them involving your attitude as a driver. The smoother you can be, the less accelerating and braking you use, the better your fuel consumption figures will be.
Some good tips here too!
IAM