Since I got married to my sailor I have been very excited about taking advantage of shopping on base! Commissaries sell items at the lowest cost possible plus a 5% surcharge. I shop there to buy a lot of our groceries. However it is not always cheapest to shop at the Commissary. They do accept coupons, but they do not double. Which makes sense, but it's still a bummer. They accept Manufacturer, and military coupons. They have year pads around the store all of the time, which are usually military store coupons. So take advantage of those. I scope the ads for the week for all our other grocery stores, making lists of what I can get on sale, with a coupon. Then everything else I need I usually pick up on base.
You can go to the DeCA website and look up your local commissary to see what sales are going on at your store as well as look up the current price for most of their goods.
Here is a great site to print out military coupons.
We also buy our gas on base, It is usually around $.10 cheaper. I also get my Sunday paper's at the gas station on base. Tax free! If you have access you should definitely take advantage of your opportunities to save!