Giant in the DC area has in-store coupon machines dispensing $1.50 off 3 boxes of kellogs cereal. You can load up on the coupons, then wait for the next good sale - like the one they had for large boxes of corn flakes at $1.69/bx. Coupon would bring it down to $1.19, which is just over 1 cent a mile. Not bad considering you also get the cereal.