Use toilet paper rolls to start your plants. When ready to plant, stick the whole roll in the ground. The roll will decompose. I've seen this with egg cartons...this would give the seedlings more root space!
Starting Seeds in Eggshells... Cute and Yes, Even Practical
Sounds like a good idea: Start your tomato seeds like this then put the whole thing in the ground when you plant them, the tomatoes will thrive off the egg shells (calcium--helping prevent blossom rot)