Outdoor brick grill - this needs some sort of area to use as a work/prep station but food tastes so much better when cooked on a real grill like this with wood or charcoal. And the cooled wood remnants can be used to add to your compost pile with the ash being used on your vegetable garden as fertilizer - so this one is a two-fer!
DIY Open Grill
Start seedlings in an egg shell and, when ready, plant the entire thing. The egg shells will naturally compost providing valuable nutrients to your plants. Cool concept!