Definately not too early to prep for the winter many winter veg need quite some time to size up.
Suggestions - carrots, beetroot Kohl Rabi(for winter storage)
Still time for peas and french beans (green frozen or dried for winter)
Still time to sow kale and purple sprouting broccoli also see if you can get plants of winter cabbages/cauliflowers (car boot, freecycle, ebay etc)
Also leek plants - a good winter standby. Onions - sown- spring/bunching types.
Chard - the winter/spring stalwart.
Winter Radishes - black skinned or "daikon" (mooli) types
Mizuna, Spinach, Turnips (roots and tops)
Plenty of inspiration there I hope :)