You know we love cellphone straps around here, so how could we resist what could be the ultimate cellphone strap ever? This one's called the Tokyo Micro garden, and contains a "nutrient-rich gel" and a plant which actually grows over time. Cool, yes, but even cooler when you smash it against a would-be-mugger's face and give him an eyeful of gel and plant matter.
The gel's called polyacrylamide. I got some on eBay cheap. It's probably that plus some fertilizer plus food colouring. And there's nothing to stop you taking it out of the vial and replanting it in a proper pot once it gets too big =) Some orchid growers sell baby orchids like that.