What's the difference between wanting something and needing something?
Mark 12:44 is the best example I can find from the Bible. It's Jesus’ conclusion about the poor widow who put two meager coins into the offering box. He says that she has given more than all the wealthy with their lavish gifts,
“for they all put in out of their surplus, but she, out of her poverty, put in all she owned, all she had to live on.”
All she had to live on - so if we are alive, if we have sufficient nutrition, protection from the elements, and medical care, we have all that we need. By extension, the things we do to gain food, water, clothing, shelter, and medicine are also necessary; if I had a stash of those things that would last the rest of my life, work wouldn't be necessary, so transportation to get to work wouldn't be necessary, and communications for talking to people I work with wouldn't be necessary….
That's all easy enough. The differences of opinion, then, arise when we start to set goals beyond living. Thriving, to use the cliché. For that reason, The Simple Dollar recommends that you study your spending through use of a budget, and make the cuts that make sense to you. I guarantee that every person you ask will have a different idea of what that means, because we all have different goals. Remember that scene from The Italian Job? A car, a stereo, a house in Spain with a room full of shoes. Set goals that you truly desire achieve and are truly attainable in your life - there's plenty of other advice out there on how to pick - and classify anything that doesn't move you toward those goals as unnecessary. If your goal is to drive a new car, do it, but be sure that it's really your goal.
Here's the thing, though: each and every moment, realize and remember that living is the only thing that truly is a need. And there is only one way to real life - Christ (John 14:6, John 17:3). Once you have the abundant life (John 10:10), living in this world isn't even necessary. “To live is Christ, and to die is gain,” writes Paul (Philippians 1:21), and he meant it. Paul gave up the good life he lived as a Pharisee among Pharisees, and decided to thrive in Christ instead. Peter understood as well - when Jesus gave a hard teaching and asked his disciples if they would leave him because of it, he replied that Christ had the only thing he needed - eternal life (John 6:68).