One of the biggest surprises I faced when moving off-campus was simply how much groceries cost. After a few trips to the store, I realized that the size of my grocery purchases weren't sustainable. My solution: decide on the things I want to cook that week before going to Ralph's - and then get the ingredients to span many meals.
I found meal planning to be a great way of bringing down the cost of food, even while being just an average cook. Make sure you're buying ingredients that don't go bad quickly and can be used for a number of different meals each week.