I had a constant supply of curly kale one year from just 5 plants. Problem is, I don't really like curly kale that much - occasionally, fine... But it was the one thing neither slugs nor pigeons liked, either!
Potatoes do well, and perpetual spinach, too. My dwarf beans are not dwarfs, but midgets - about 10 cm high by now, and they've been in for many weeks! And my (supposedly) normal peas have so far produced a handful of mangetout.
I'm hoping for courgettes, and pumpkins!
Ina