We usually do all our grocery shopping at the Giant's store nearby. There are a lot of grocery stores like safeway, trader joe's, whole foods very close by too, but we stick to one store as it maximizes our savings.
Giants has a promotion where you earn a point for every dollar spent, and sometimes additional points for buying certain items. 100 points save you 10¢/gallon on gas at any Shell gas station, 200 saves you 20¢/gallon and so on (http://www.giantfood.com/savings/shell_program.htm). On an average we spend around $200-$300 on groceries, so we make sure to go to the giants store every time. Gas prices are about 10 - 15 ¢ cheaper around where i work than near the apartment, so by going to a shell gas station near work and using the giants card savings, we save about 30-45 ¢ per gallon on gas, that is 12 - 18% discount on every gallon of gas used, which is pretty sweet in my opinion.
Plus i have a chase credit card which gives 3% cash back on gas, and currently the chase freedom card gives a 5% cash back on groceries. Add these cash back offers in, and we save a good deal on groceries and gas every month just by being a little smart and keeping a mental tab of where to buy things which is not very difficult to do.