I am doing the Dave Ramsey debt snowball.
I have canceled my 401K contributions, my 529 contributions, and altered my W4 exemptions. What else can I do to save on expenses so I have more money to put toward my debt?
The debt snowball approach is a good way to reduce debt. What concerns me most about your question is that it seems you are cutting out investments, rather than exploring ways to free up money through savings.
Even when people are getting out of debt, I hate to see them stop 401K contributions if they are then losing out of employer matching deposits.
I would take a close look at all of your statements, including your cell phone bill. Take a good look at the plan you are on for example and see if you can drop to a lower plan without having to pay for minutes. If you are paying for extra minutes, go to a higher plan or cut back on your calls.
Look at every other expense you have. Shop for cheaper car insurance, home insurance, and even consider raising your health insurance deductibles if you could cover the deductible in an emergency. Higher deductibles mean lower monthly rates.
Look at the cable bill, shop for cheaper internet access, etc. It is always worth evaluating current services to see if new lower rates are available.
Typically the largest monthly expenses are for transportation and shelter. This is a bit more radical but have you considered trading down in those areas to free up additional money?
Every dollar saved is a dollar that does not have to be earned.