Since I don't have a car, I only use gas for the lawn mower. I'm stretching that out a few days longer between mowings though. Can't pass up a good excuse!
One thing I am doing, is keeping a much closer eye on my bike when it's parked! I figure the odds of theft increase with the price of gas.
Something I've always tended to do, is keep a grocery list.
IF I happen to be going by the grocery store for some other reason, I'll stop in on the way home and pick up a couple items that I can carry easily, to reduce the amount of trips with an uncomfortably heavy load.