Posted: 18/04/2016 at 10:51
Hardy geraniums, hostas, brunnera, pulmonaria, primulas, lily of the valley, campanulas and some other perennials should divide nicely now. If you (friends / family) have a clump or two of any of those you can spare you might well be able to 'make' several smaller plants to put into 3" pots.
You could also consider buying a couple of large pelargoniums and striking multiple cuttings from them. Penstemon cuttings might also have taken by then (depends when the fete is). A large pot of supermarket parsley will also subdivide into about a dozen smaller plants which will be a good size if you do it now.
In terms of seeds - I would go for perennials like dahlias, lupins, coreopsis & nepeta. Also herbs (chives, coriander, parsley, basil, dill)
With the possible exception of sweet peas I wouldn't spend time sowing bedding plants. Most people have their pots etc sorted out by June / July which is when I assume you will be holding the fete.