There's a difference between owing money on a loan, and being truly in debt.
If you are in true debt, don't spend what cash you have on hand. Even if you don't feel like paying back the bank (which really confuses me, as a negative balance will compound greatly if left unpaid), but have cash, just hang onto it. What happens if you break something on the car or if you need quick money in a hurry for something unexpected? You're going to have to sell that brand new exhaust at a loss, and have to wait until someone else wants to buy it.
So in other words, if you want to throw cash at an exhaust you very well may have to get rid of soon, then fine. But the SMART thing to do would be to get all your important financial matters squared away so you don't ruin your credit and your financial standing for years to come.
