Hello there!
live plants are great in the cage. I personally like the ficus tree. you can find small ones that will fit in your cage for around $15-19 at Homedepot. Save your receipt just in case. They will replace your tree if it dies within a year.
I usually take the tree out once it doesn't fit in the cage, and plant it in a larger pot. When it is sunny out (which is quite often in San Diego), I take my chameleons to hang out on the larger trees on my Balcony or my back yard.
I watch the sky for Red tail hawks and Falcons because they like to hunt near the area I live in. At the sign of any large bird, I take them back into their cages.