The size of a challenge should never be measured by what we have to offer. It will never be enough. Furthermore, provision is God's responsibility, not ours. We are merely called to commit what we have - even if it's no more than a sack lunch.
At least one indication of unbelief is the tendency to measure life's challenges against our own adequacy instead of God's promises. To enter our Sabbath rest, we must put an end to self-reliance - trusting in our own abilities to overcome difficulties, rise above challenges, escape tragedies, or achieve personal greatness.
Next time you're faced with a credit-purchase decision, wait. Don't say no necessarily. Just wait. I challenge you to present your need to the Lord before presenting it to a bank, and see what He does with it.