Hi Kim
You can always intercrop with fast growing salads - lettuce, spring onions, radish etc.
With a fairly limited plot in terms of space, you may be best to concentrate on 'high value' vegetables - rather than basics like potatoes. What's high value will depend on what you like.
In terms of production for space, vertical growing is best - things like climbing french and runner beans give an awful lot from a small space.
I met a chap at the NVS who covers most of his vegetable needs from less space - but it was on a deep bed and the soil was both deep and rich. He had a lot of things brought on in pots before planting.