Business Casual Dress for Men

Basics
Khaki pants, neatly pressed, and a pressed long-sleeved, buttoned solid shirt are safe for both men and women.  Polo/golf shirts, unwrinkled, are an appropriate choice if you know the environment will be quite casual, outdoors or in a very hot location.  This may not seem like terribly exciting attire, but you are not trying to stand out for your cutting edge look, but for your good judgment in a business environment.

Shoes and Belt
Wear a leather belt and leather shoes.  Athletic shoes are inappropriate.

Cost and 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. 

Ties
Ties are generally not necessary for business casual, but if you are in doubt, you can wear a tie.  It never hurts to slightly overdress; by dressing nicely, you pay a compliment to your host.  You can always wear the tie and discreetly walk by the room where the function is held; if no one else is wearing a tie, you can discreetly remove yours.

Shirts
Long-sleeved shirts are considered dressier than short-sleeved and are appropriate even in summer.  Choosing white or light blue solid, or conservative stripes is your safest bet.  Polo shirts (tucked in, of course) are acceptable in more casual situations.

Socks
Wear dark socks, mid-calf length so no skin is visible when you sit down.

Shoes
Leather shoes should be worn.  No sandals, athletic shoes or hiking boots.

Facial hair
Just as with interviews: Facial hair, if worn, should be well-groomed.  Know your industry and how conservative it is; observe men in your industry if you are unsure what's appropriate or are considering changing your look.

Jewelry
Wear a conservative watch.  If you choose to wear other jewelry, be conservative.  Removing earrings is safest.  For conservative industries, don't wear earrings.  Observe other men in your industry to see what is acceptable. 

Hair
Should be clean and neat.

Shoes
Should be in polished condition.  Make sure heels are not worn.

Details
No missing buttons, no lint; and don't forget to remove external tags and tacking stitches from new clothes.

Hands
Clean fingernails.

Fit
Clothes should be clean, neatly pressed, and fit properly, neither tight nor baggy.

Smell
Cologne should be used sparingly or not at all.  No odors on clothes.  Don't smell like smoke.

Padfolios
Preferred over a bulky briefcase.  A small briefcase is also appropriate, but if you have no reason to carry a briefcase, don't; you risk looking silly.

Bookbags
Appropriate to carry to an information session held on campus (after all, you are a student).  For career fairs and job fairs, bookbags are generally checked at the door, and you should carry a padfolio only.  Don't carry a bookbag to an event held at a hotel.