The first is eggshells. Organic Gardening suggest drying the shells out on a baking pan using the lowest oven setting, then pulverizing them in a food processor.
This leaves you with powder that can be sprinkled around base of your houseplants. It is a great source of calcium (chicken eggs are 93 percent calcium carbonate), and also a great way to raise the pH levels if your soil is too acidic.
The second is coffee grounds. They will give your plants a 'jolt' of nitrogen, phosphorus and potassium and are perfect for plants that like acidic soil.
Both make use of ingredients that served their use to make a free, natural plant fertilizer. The idea of drying and pulverizing the eggshells would also make them easy to store and share.
I actually got a Compost turner for a Christmas present and I am planning in the next couple of days to turn my compost pile. Dad gave me a demo on his own compost and it worked Really Well. But it is important to add the right things to your pile!