A lovely tradition I've heard about here is to give a sprig of Lily of the Valley to your neighbours (or loved ones) on 1st May. I've been safeguarding my little batch for just that purpose.
Apparently since its introduction to Europe from Japan during the Middle Ages, Celtic folk believe lily-of-the-valley to be a lucky charm.
The French tradition of giving lily-of-the-valley flowers on May Day is supposed to have begun on May 1st, 1561, when King Charles IX of France was presented with a bunch of the flowers as a token of luck and prosperity for the coming year.
Does anyone else know of other local customs it would be nice to join in with?