Grow carrots in a 2 liter soda bottle. Great idea for kids. They could watch the roots & tops grow at the same time.
16 Plants that Regrow from Kitchen Scraps
from lemon seeds
Permaculture Ideas: Foods that will Re-Grow from your Kitchen Scraps
Indoor herb garden
FarmTina: Green Thumb Conundrums: How to Harvest Your Container Herb Garden