Cucumbers are brilliant! We've had great success with them every year we've tried. This year I managed to save some seeds from them too.

Have you tried growing beans in pots? They can be very productive. I grow potatoes in old cardboard boxes and they're pretty effective.

Also, auntsarentgents & I have a gardening community called seedclub, which has been a bit quiet lately; you'd be welcome to join if you're interested in swapping seeds and ideas, and talking about your garden.