Spray oil
Most of us when we're cooking with oil, use about a tablespoon. This is around 100 calories and most of that goes in trying to get the oil to be even before you place your food on top. But opting for a spray oil means you only use one calorie per spray and it's even.
To cook up a spag-bol or a stir-fry you'll only need about 5 sprays, so you've already saved yourself 95 calories. Better still is using a non stick pan.