The amount of gas used for cooking is negligible compared to that used for heating. I cook with gas every day (but I've got electric heating). My last gas bill was for around �6 for 3 months, so that's only about 50p per week. I might save a few pence on my gas bill by buying decent steak, rather than Tesco's 'Value' mince but I'd put my weekly food bill up from around a tenner per week to a figure many times that.