Think about a candle. It has a relatively short "life," yet we cannot say the candle has no purpose just because it is ultimately burned up and gone.
Our life is similar to the candle. We don't last too long, then we're gone. But like the candle, while we're here we can serve a purpose; we can bring light (wisdom) and heat (passion) into the world.
Many JWs I knew in my long-ago youth would have said the purpose in life was to "be happy." I still think that is right, and even more so when you take a dictatorial band of hypocritical theocrats out of the picture.
"God" does NOT need your money, you do. If your comfortable, find a cause you support and do what you can. If you are physically able, give some of your energy to a cause you believe in. Here are some you can consider: Doctors Without Borders, aid for wounded veterans, children's hospitals, animal rescue/welfare, legal justice, and religious charities. Even though I am not a Believer, I donate to religious charities because they are usually more effective at getting money to where it is needed, unlike many quasi-scam popular "charities." You can get information online about which charities are most efficient.
Let us know what you discover within yourself.