I now do a supermarket shop once every 2 weeks instead of every week, and if I run out of something, I just go to a little local store. That way, because of their higher prices, I only by the really essential items. Our supermarket is around 20kms away, and I drive a gas guzzler, so any savings on fuel are worth while, and it means I dont buy extra treats.
Also, when I make my list, I try and stick to it. If I see any "bargains" at the shops, I stop and ask myself "now do I really NEED this". Then I go away and think about it before putting it in the trolley. Ive also started saving money off coupons, which is something I didnt do before.