To begin growing your own food, you need to craft a planter. Currently, you can only craft a small one. Craft it and place it, and keep an eye out on your inventory each time you collect a barrel. You might get a potato, or a beet. You can plant these two plants in the small planter, and like all plants, they need fresh water (see below). Give the watered plants time, and stay near them, as seagulls will try and eat them. You will get more plants back than you planted, making this a renewable source of food, albeit time consuming.