If you are visiting Palo Alto, San Francisco, Oakland, or anywhere else in this general area, and you are interested in active outdoor activities such as hiking, kayaking, horseriding, etc., the Outdoor Adventure Club offers many activities year round. I am not a member, but I have been on several enjoyable kayaking trips with the club. Costs for activities are usually from $40 to $150 for a day trip and more for an overnight trip.
Equipment: Depending on the activity, you may need a rain jacket, swimsuit, appropriate shoes, etc. You may also need to have transportation to a meeting point although there are some opportunities at times to ride with someone else who is going to the event. Usually the major equipment (such as a kayak and life jacket) is provided and often lunch is provided as well.