Backup Your Files
This seems really obvious, but a lot of people screw this up. Write it into your calendar if need be. Get an automatic online backup if you don't want to bother doing it yourself regularly. Computers are pushed to their limits, and they frequently crash. Protect yourself from a disaster!
Large Format Printers
You'll probably print more 11x17s than any other paper size. Get a large-format printer. It will be a lot easier if you don't have to go to the computer lab or print shop each time. These printers can be a little expensive, but they do go on sale frequently. If you've got a considerable chunk of cash, consider getting a plotter too.