I'd go for a quick green leafy crop, silverbeet, kale or spinach in the winter, lettuce or rocket in the summer. Those are all shallow rooted and will recover from being too hot and dry for a day if you water them well. They do all require watering, preferably daily when it's hot. They will all go to seed if you let them, and easily produce fertile seeds. I did that deliberately with ours to save buying seed next year. You can trim kale at almost ground level once it's established and it will grow back, or just keep pulling leaves off and you can end up with quite a stump. The others are normally annuals.
Our kale and silverbeet both grew quite well through a Sydney summer with regular days over 35°C and a few over 40°C, while the lettuce and rocket went completely wild. We went on holiday for a few weeks and came back to a wall of metre-high rocket all gone to seed and now it's growing wild. Which is good, since we have stupid lawn and enough space that having edible rocket as our broad-leafed "weed" makes me happy :)