Weight reduction reduces fuel consumption & increases speed so it's win-win.
Probably covered before but wanted a definitive list.
Remove spare tyre
Remove safety triangle
Remove first aid kit
Remove 6CD changer
Remove floor mats
Remove sound insulation
Remove air conditioning
Put yourself on a diet
Lightweight wheels and tyres
Smaller back box (or straight pipe)
Lightweight radiators (all over ebay but with no mention of weight?)
Comment on practicality, and please add.