If you eat eggs, you've got eggshells. In our case, we have a lot of eggshells because of our homestead chickens. This is a valuable resource that everyone can reuse. I know, eggshells maybe aren't the first thing you may think of when recycling, but to me, it's the best! Eggshells are full of calcium, protein and minerals and can be used for so many things.
If you dry them for a week, then crush with a potato masher (that's what I use), you can put them in the garden to deter pests such as snails or slugs (they won't travel over the eggshells). And, after crushing with a potato masher, I put them in the blender to make a powder. When transplanting tomatoes, just put some powder into the ground before planting and it will keep blossom rot away (it's caused by a calcium deficiency). I also add this calcium powder to soil and compost for a potting soil when starting off seedlings. Of course, putting eggshells in your compost pile is beneficial, but if you don't have a compost pile, you can put the powder directly in the soil. You could make a calcium tea for trees (I use it for our apple tree seedlings) instead of spraying them with chemicals by sitting the powder in water for a few days and then feeding the trees. If you have houseplants you can put the eggshells in a mason jar (or watering can), and feed your plants (a natural fertilizer).
The best eggshells are from chickens that you already know, but not everyone has access to farm fresh eggs, although it may be worth searching for in your area. Check out the local farmer's market or go for a drive in the country, often farmers will post a sign offering farm fresh eggs. It really isn't that much more extra work to keep the eggshells, let them dry and add them to your plant food or garden. It's just another thing that you can do to become a little bit more self sufficient.