What survives and pretty much thrives in the worst drought? We're in Exceptional Drought, pretty much in some stage of drought since 2006. What I can think of offhand are plants like Esperanza, Cenizo, Mexican Firebush, Woolly Ironweed, Lace Cactus, Red Yucca, Desert Willow, Anacacho Orchid Tree, Four-nerve Daisy and gayfeather. But even some of my most reliable plants are going dormant in some form, some just not blooming or growing at all unless they get rain for a while, assuming they are not watered.
My new best friends are dragon fruit. A lot of the epis (see the Cactus Flower Forum) seem to survive with minimal water. I have two small plants I got at a plant depot place about a yeqr ago and they are hanging in with only occasional water.
Plumerias also hold up well with little water. My tulsi basil thrives and reseeds itself.
Do you have freezes where you are? That would make a difference.
Also, you might check out the self-contained box garden forum You can make an Earthbox-like container for less than $5.00
Yes, it does freeze here...we live in the hills, so winter can be pretty cold. The last couple of years we haven't had anything below 20°, but some years it gets lower. I've heard of earth-boxes, but don't know anything about them really. How are they used in drought areas? Some of the local native plants are pretty tough, and I do like the natives.