Another sharing type project I've found rewarding: a few years back, I joined a timebank. Timebanks are located across the country (maybe the world?). The basic premise is that people "bank" however many hours they spend doing things for other timebank members, then when a member needs something done, they utilize their accumulated credit hours. You might ask for or give a ride to the airport, have someone check in on a relative or feed an animal while you're out of town, etc. One person's hour is valued the same as every other person's hour.
The people in my particular timebank tend towards a little older, maybe b/c older people generally have more time. But I don't think that's necessarily true of all timebank groups. Our group has a potluck dinner once a month, which members attend or not as they choose. Potluck attendance earns 2 timebank hour credits, as it is felt that the interchange allows members to get to know one another and learn what other members have to offer in terms of using your credits. Also, we charge $20 a year for membership (mainly to buy insurance), and for which members are allowed to take 2 timebank hour credits.
This past Sunday, we held a "many hands" project in which about 10 people went to a member's house and cleared brush and leaves from his 3 acres for a few hours. He is an electrician who has helped many of our members with their wiring (obviously a much-valued skill), and has an illness which has a 5 month recovery time, so hasn't been able to keep up his yard. Afterwards, his wife invited us all inside for homemade soup and desserts.
Timebanking is another activity which can not only save people some money, but builds community. I've been very happy that I became involved with my timebank, even though it's in the next county (my county doesn't have one and I'm too lazy to start one), so it's a little far for me.