Grow an Avocado Tree from the pit (for a houseplant, it probably won't produce fruit). After drying, the pit is suspended in a glass of water and once there is root growth of about 2″, it can be planted in a pot of soil and tended to as a houseplant. If your climate allows, you can plant this outdoors.
More good gardening stuff: "Growing lettuce on your porch. Plant seeds in succession about a week apart, that way you'll have greens all summer."