These planters mainly came out of my recycle bin, or were rescued from the trash can, and almost all of them were previously used to store food, so they shouldn't contain any harmful chemicals.
Step 1: Egg Carton Seeds
Since I already have a lot of seeds started, and am running out of window sill space I don't have a real picture of an egg carton planter, but I will explain as best I can, with the help of the picture.
Cut the cover/top off, then fill one or both sides with dirt or potting soil and plant your seeds. Easy as a mud pie.
The best egg cartons to use for this are the cardboard type ones, as you can just cut off the bottoms and put it straight into the ground when it's time to get it outside. (Of course you could do the same with plastic or styrofoam ones, but it's not very eco)
Step 2: Milk/Cream Carton
Pros- Mostly Waterproof because they had liquid in them before.
Cons- If you don't tape up the top side really well it leaks.