Here's a bit about my life story through grad school, and the important details correspond to the experiences of a few friends and colleagues:

I was a grad student in physical sciences at UCB – on the university payroll/stipend (although the following applied to students on grants as well). Living on low cash flow with high rents an expenses eventually got me (dumbly) into credit card debt. I could have avoided getting into this debt by anticipating the need for student loans, but I wasn't paying attention. Actually, I wasn't even aware that I would qualify for student loans considering that I was getting a paycheck. As a personal note, in my case I wasn't driven into the red with simple reckless spending, I also had a kid. Although, it can be argued that this is also reckless – certainly discretionary – spending…

The important fact is that school loans are available. If for some reason you are in disbelief, the basic idea is that some of our humanities friends must cover their way through grad school on loans, as do nearly all of our law-school and med-school buddies. The University, or more correctly the federal government (who's giving you the money) doesn't really take into account what you're studying, and not even how much grant/stipend you're on. Perhaps they should take into account your paycheck, and maybe if you fill out the paperwork with all due earnest diligence they do take this into account, but in practice, I've known of no student who had any trouble getting any loans. If you think of it in another way, graduate students are relatively safe investments for the lender, so they are likely to make their money back when students become professionals and start paying the loans back. What I've determined through anecdotal evidence is that the biggest factor in how much cash is available to you is how much you've already taken out in Perkins and Stafford loans in, for example, undergrad.

After hearing all of this information from a few friends, I filed for financial aid for the first time in grad school. My colleagues with ~$20-30K undergrad financial aid have done the same in graduate school with the same results: You find out that you can borrow about $8k/semester without much of a hassle, and a significant fraction of that may be subsidized loans. If you are responsible, you take out the bare minimum (as the paperwork advises) to cover your expenses and the necessities. But, if you're brave or thoughtful and diligent, you pay off other higher interest debt. In my case I took out student loans to completely pay off my credit-card debt, and then the Department of Education purchased a used VW for me. If you're particularly clever and good with finances, you cam take out money to make more money, but then again, for some this could require enough time, thought and effort to make it not worthwhile. To get back to my particular case, a student loan simply had a way better interest rate than what I could get with a used-car loan, particularly considering my credit-card debt situation.

In the end I could consolidate ~$30k at _FIXED_ 2.78% APR, which was better than the car loan, and WAY better than that credit cards. I don't believe you can get this fixed rate anymore, but whatever the current rate for student loans are is still pretty good. Taking out a bit of extra cash also allows you go out to dinner and/or buy yourself a pair of jeans for hanging out with your professional friends who live in the city… but then again, you don't want to get into reckless spending. If you just simply can't live within your stipendy means, then I strongly recommend estimating your needs, and covering them with student loans and not credit cards. Along the lines of a rainy day fund, it is also nice to have about $2000 sitting around so that when you go to that conference in Europe or South America, you can pay off the damage before if the reimbursement process takes too long – and it will. It might only happen once a year, or maybe once it graduate school, but it will help you save on the fees and help pay off other emergency expenses as well.