in another kitchen garden mag, there was an article about a chap who grows all his veg in pots & tubs. Also, we've hard threads about growin spuds in bags (this is a show/grow method) so I think the following would be a start

Spuds 3 per entry 1 class coloured & 1 white.

You cold grow onions in flower buckets so there's another.

Short Carrots Or other than long I think they are called) you could grow these in tubs

I've never showed veg so I couldn't say how they would turn out but it would be a giggle.

ntg