There are probably some good ideas in other replies. Having purpose in life is everything (I think). I suggest building humanity through learning and service, and hopefully coming to know eternal truths that support that learning & service in the best ways. I wrote my further thoughts here (a simple site, that I hope is skimmable, allowing one to drill into whatever parts are more interesting, for more details, no cookies etc etc): http://lukecall.net/e-9223372036854588981.html .

All the best to you.

Edit: ps: one volunteering site that doesn't require you to figure out detailed extensive plans before getting started, is probably https://justserve.org . They let orgs and volunteers sign up and see what is available, for a given locality.