Shoes / belt:
Wear a leather belt and leather shoes. Athletic shoes are inappropriate.
Cost / quality:
You are not expected to be able to afford the same clothing as a corporate CEO. However, do invest in quality that will look appropriate during your first two or three years on the job for a business casual environment or occasions.
Details:
Everything should be clean, well pressed, and not show wear. Even the nicest khakis after 100 washings may not be your best choice for a reception. Carefully inspect new clothes for tags, and all clothes for dangling threads, etc. (as with interview attire).
Use common sense.
If there are six inches of snow on the ground and/or you are rushing to get to an information session between classes and you left home 12 hours earlier, no one will expect you to show up looking ready for a photo shoot — they'll just be happy you made it. Just avoid wearing your worst gym clothes and jeans. If you show up at an event and realize you're not as well dressed as you should be, make a quick, pleasant apology and make a good impression with your interpersonal skills and intelligent questions.