A teaching of Jesus' during The Sermon on the Mount
There's a lot of wisdom in these teachings:
Jesus tells us that we cannot have two masters; that we cannot follow both God and money. It has certainly been my experience that people who are devoted to money are somehow less happy than those to whom money is just a thing, not a central theme to their lives.
Jesus then tells us to not worry about money. The birds and flowers don't, yet God provides for them. This can seem somewhat naive in today's world, but I think the central message of not letting money rule your world still holds true.
Jesus also tells us not to worry about possessions. Why worry about clothes; no clothing is as beautiful as a flower, so why worry about what clothes you are wearing?
Jesus then tells us not to worry about the future. Plan for the future, but don't worry about it - don't unneccessarily burden yourself in the present.