April showers may bring May flowers, but they also bring blanket parties and picnics. Tourists turn their cars into caravans; appetites become finicky and so mothers pack the roast beef, bread and fruit into a basket, place the salad in a jar and wrap the casserole ,of vegetables in a paper; then off they go to the woods to picnic. Young couples and gay parties build bonfires and roast steak and bacon over the coals. The hostess, tired after the strenuous winter social season, turns the bored luncheon or dinner party into a picnic, and everyone is gloriously happy and informal.