One of the most informative books available on the subject is "Snow Sense" by Jill Fredstrom and Doug Fessler. These two are the former directors of the Alaska Mountain Safety Center. They are world renown experts on avalanches and are used as technical experts on many skiing movies and documentaries.
Take an avalanche and backcountry survival course. Maybe more importantly, make sure your riding partners take one. If they won't, get new partners. If you get caught in an avalanche, no one is going to come in and save you. It will have to be the guys and gals you ride with. And they have to know how to do it, and do it right.
Equipment for EACH PERSON in the group:
Beacon, Probe and Shovel
Equipment divided AMONG the group:
Extra tools (pit shovel and handsaw)
Candles (heat, light and melting snow), Fire starting kit (magnesium chips...)
First Aid Kit--Signal Aids (The new laser lights are cool)
Cellphone or Radio