In the city you can't really plant a tree like we used to back at my private elementary school on earth day. There's really no where to plant one and I'm pretty sure it's illegal.
But almost anyone can have an herb garden. Jim and I did for a while until our green thumbs turned into bored thumbs and we decided the garden didn't have to make the move. Still, it was really fulfilling to use hand grown dill on your scrambled eggs–and if you care about pesticides and organic stuff, nothing could please you more.