I think everyone should have something they feel passionate about. It can be anything. Take my sister, Christine, whose cause is animals. She supports local animal shelters where ever she lives, she serves as a "foster parent" for animals waiting to find homes and she does what she can to spread awareness about animal cruelty. All this while being an awesome mom to my nephews.
In LDS Scripture, Doctrine & Covenants Section 58 Verse 27 says, "...men should be anxiously engaged in a good cause, and do many things of their own free will, and bring to pass much righteousness." Having a cause to believe in doesn't mean you have to drop everything, drain your bank account with donations, march in every parade and squat at every scheduled sit-in (though I think an occasional act of non-violent demonstration is good for the soul).
Having a cause can be as simple as making a minor lifestyle change or thinking differently about how you go about doing ordinary things. From simple things like recycling to participating in local food drives.
Another example of having a cause that's simple but beneficial is that of a family I know in Sanpete County that decided to build a straw-bale home. Straw-bale homes use straw instead of fiberglass for insulation. And instead of covering their outer walls with pressboard or vynil siding, they use homemade plaster made from clay, sand, wheat-paste and straw to stucco both the outside and inside of their home. The cost difference isn't great but there's a great deal of satisfaction in knowing natural materials from the earth are being used instead of materials that require manufacturing and a great deal of energy to make before it even gets to the job site.
The causes that I believe in are education, the arts, veterans issues and healthcare. For education and the arts, I channel my efforts through my the profit Utah Filmmakers Association. I address my veteran and healthcare concerns by doing my best to be informed about them and posting my thoughts and opinions on this web site and by writing letters to newspaper editors. Ya see, simple things. My method of choice is exercising my right to freedom of expression which, in turn, fosters awareness. And awareness of a problem is the first step in solving it. Of course, pointing out a problem should always be balanced with offering a solution