Lettuce - sow little and often. If you really need 30 lettuces in one week then sow 30 on one day - most of us don't.
I put a succession sowing seed pack together, includes lettuce, spring onions, beetroot, radishes, pak chio, Kohl rabi and other short season veg together and sow a small row every fortnight. Give you a longer season. Beets and radishes, take the larger ones, and leave the smaller ones to keep growing. Radishes that go to seed, pick the pods and have them in stir fries etc.
Aubreys - greenhouse or poly only I am afraid.
Potatoes - should all be out now but they go green if not out of sunlight so work on more mulching next time.
tomatoes - indoors are best but my outdoor ones have only just started colouring.
Planning what to grow, mixing up your varieties, sowing little and often will help.
Grow some perennials, strawbs, rasps and other fruits can make a huge dent in your diet. Also, look at french beans that can be eaten green, shelled or dried - and grow up so take up little room. Bunching onions can be left in the ground, just taking some when you need it.
Try looking at a detailed planner, such as the schools ones on Garden Orgnaic's website www.gardenorganic.org.uk/schools A35 gives you a good breakdown of what you can grow and when you need to do stuff.
For now - you can sow winter crops as we still have time, or go to a garden centre and see what veg is being sold; if you can't find any then sow some green manures and do more planning for next season.
Overwintering onions, garlics, leeks, brassicas eg kales, winter lettuces, pak choi etc can all go in now if you get hold of the seedlings/cloves/bulbs.