What situations will disqualify you from getting a security clearance?

If poor money management will disqualify you from a security clearance, why do congress people spend millions of dollars to get a job that pays about 200 thousand a year??

If you want clear and correct answers I recommend you take some time and go talk to your S2/SSO. They should be able to answer all your questions and even help you start the paperwork. But to answer your question no. Just be honest with anything you get asked. If you did drugs in the past then tell them. When you get investigated it really is about will you be honest and do you have any ties to an enemy. The form you will fill out is the SF86. You can take a look at it and even start gathering the information to prepare for when you actually need it. But I still stand by my original answer... See your units S2/SSO.

The problem with bad credit in a Special Background Investigation is that it highlights at least two potential problems: 1 - that you are irresponsible with money, and 2 - that you are vulnerable to blackmail and / or corruption. The way to defuse the matter is to identify exactly why you have bad credit. If it is because you were kiting bad checks you're in real trouble. That's a felony and, while they probably won't prosecute you, they certainly won't clear you. If it's because you got in over your head with debt, then as long as you have the situation under control now and you are not likely to get in that bother again, you might be okay.
When you fill in your security questionnaire there is a block where you can explain things that you think might be problematic. This is where you want to tell the investigators what the problem was and what you have done to rectify it. They'll check the facts and go from there.
CW3 J.D. Walker had it absolutely right, though. You cannot lie or even embellish the truth a little. If they are even thinking about giving you a clearance (that is, if they don't deny it outright) they will interview you about it. Be absolutely and completely honest. Tell them everything. If you hold something back and they find it out for themselves, your goose is cooked and your clearance is a no-go.
Good luck brother.