I've got some for you, feel free to use:
1. Spring onions. I put the onions I bought but I didn't use in a flower pot. I get a stick, make a hole, put the spring onion in the hole. Works the same for leeks too. I water them like regular onions I planted from seed and harvest when needed. Also the ends, you can try to replant the part with the root attached and regrow a new onion.
2. Lemongrass. I now can see the lemongrass I bought from the warehouse area over on Florida took root in the flower pot. What I did was buy two stalks of lemongras that looked like it was cut close to the root and stuck them in some dirt in a pot. Well it has taken several months but it looks like they've taken root.
3. Pansies and impatiens- Buy them from the big box store or other spot. Cut off all the flowers because heaven knows what's been sprayed on them. Plant them and new flowers should be edible for garnishes.
4. Purslane- Get the seed, this stuff grows easy in DC (particulary between sidewalk cracks), and doesn't take much effort on your part. It is considered a weed by many. A very tasty weed, yummy with a nice lime juice and garlic dressing.