Keep egg shells in open container in fridge. When the container is full, crush shells into small bits and sprinkle them around base of your plants. Sharp eggshells will deter slugs, snails other bugs & adds touch of calcium to soil.
Tomatoes need calcium to achieve their full flavor potential. When planting tomato plants crush up (to powder) about 4 or 5 egg shells and put them in the bottom of the hole. Then plant tomato on top. They'll provide calcium and prevent blossom end rot.