This recipe, from the now classic Silver Palate Cookbook by Julee Rosso and Sheila Lukins, goes considerably further than the traditional three-bean salad.  The fact that it shouldn't be served chilled makes it more likely to arrive at the picnic site at the right temperature.  The fresh green beans are a nice touch, but if you're in a hurry canned ones could be substituted.  If you're concerned about the raw egg yolk in the dressing, you can substitute two hard cooked yolks, but the texture of the dressing will not be the same.

Ingredients:

1 can (1 pound) garbanzos
1 can (1 pound) white kidney beans
1 can (1 pound) red kidney beans
1 can (1 pound) baby lima beans
1 can (1 pound) black-eyed peas
1 pound fresh green beans (or half green and half yellow wax beans)
1 egg yolk
1/3 cup red wine vinegar
1 tablespoon sugar
1 tablespoon chopped garlic
salt and pepper to taste
1 cup olive oil
1 cup chopped green onions
1/2 cup chopped Italian parsley

Directions:

Drain canned beans, rinse thoroughly in water, and drain again.  Cook fresh beans uncovered in boiling salted water until done but still crunchy.   Cool beans in ice water.  Drain, pat dry, and cut into 2-inch lengths.  Toss canned and fresh beans together in large bowl.  Combine egg yolk, vinegar, sugar, garlic, and salt and pepper in bowl of food processor fitted with a steel blade.  Process briefly.  With motor running slowly dribble in olive oil.  Pour dressing over beans, add onions, and toss.  Cover and refrigerate overnight.  Garnish with parsley and serve at room temperature.