I always grow cabbage family in pots first as they can get eaten off by so many things. I grow for a veg box scheme and cabbage family that do well from later sowings include spring cabbage and kale, rocket, chinese cabage, brocolli raab and you could also try turnips and mooli, although these might work better from the ground. Not too late for lettuce either, and by Sept you can start on onions, garlic and later broad beans (Nov in Norfolk).
Have fun.... and if your pennies ever allow it, a polytunnel means you can have veg all year round. We don't buy any at all....and eat a largely veggie diet...