There are lots of uses for egg cartons, and one I use them for is planting seeds (poke a hole in the bottom for drainage). If they are small vegetables, like radishes, you can plant the whole biodegradable (pulp paper) carton into the soil or cut each dome and plant separately.
Other ideas for egg cartons:
Storing Christmas ornaments
Use for packing items to mail
Use in a desk drawer for paperclips, fasteners etc.
Store jewelry (the clear plastic ones work best for storage)