Get a growbag now, cut out most of the top side and sow a packet of mixed Japanese salad leaves such as Mizuna, Mustard & others. These leaves are hardier than summer salad leaves and I've grown them outdoors during the winter in sunny sheltered spot. In another growbag you could sow Swiss Chard, which is a green leaf vegetable similar to spinach which will probably keep growing through autumn & winter in a greenhouse.
Next spring you can make can early start with peppers, chillis, tomatoes, aubergines,courgettes and cucumbers.