Many items can be reused and repurposed for seed starting containers. Empty cardboard egg cartons, and even egg shells themselves make great little seed starting pots - and can be popped right into the garden at planting time!
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.