For my spinach seedlings: Grow seedlings in recycled containers as greenhouses. Any clear plastic container will do. Use paper towel rolls or toilet paper rolls as a pot. When ready to plant, simply place the whole roll in the ground and plant.
Planting seeds in eggshells then put eggshell and all in garden bed when ready for transplant. Crush egg shell a little to give roots room to expand and gives an added benefit of nutrients to the plant.