Usually a good boarding school has a student service office (or guidance office) that can offer useful advice on volunteering works and other meaningful activities at school and beyond especially in relations with college application process. Student groups or faculty members also would organize some volunteer works in the school as well. My first advice is to find or to even organize your own volunteer activities in school while finding some supports from the school. Please remember it is not easy to start something new and even to continue to develop. Many colleges nevertheless would like to see this type of projects led by students, and particularly are interested in what kind of volunteer works a student participates and in what capacity he/she participates. Clearly it is not about the size of organization or the number of volunteer works you involve, but about how much you put your hearts in particular projects. Please start anything even that is small within the school community if possible.
Still if you cannot find anything inside the school, then you might want to go and find something meaningful outside the school. This could be more complicated since you are at the boarding school. You might need to seek a permit from the school, to arrange your own transportation, and to find other logistics to support your projects. I think that your idea to leave the school and to live with a host family (I am not sure if your school would allow this) for community service is not wise because you are there to experience the wholesome experience that a boarding school can provide. I am sure there are plenty opportunities for you to participate meaningful activities which also boost your college application nearby Stanford University while you are staying at your school. Good luck! Prime Global.