Eggshells, cups, cans, even milk cartons can be made into seed starters. And don't forget the farmer's helper. Did you know there are over 1000 species of earthworms. Darwin studied earthworms extensively and deemed them essential to agriculture and human existance. Pretty deep.
To make your own worm farm, cut off the top of a two liter plastic bottle, about right at the top of the soda label. I poked a few holes in the bottom for drainage and added a bit of sand, soil, and some strips of newspaper I had soaked in water and squeezed out the excess water from.
Add worms, a piece of lettuce or other vegetable scraps, and keep moist. Worms love the dark so I used black paper taped to form a cylinder to keep the worms in the dark. Feed them often and keep the soil moist. After a few days you'll be able to see the worm tracks and castings as they recycle their food! Add the soil to your garden.