Basically, Steampunk combines a fascination with the Victorian age and invention, including inventions that didn't happen until well after the Victorian age and a do-it-yourself, anti-mass production mentality. It's the Victorian age that might have been, but wasn't, kind of like a Jules Verne novel come to life. If you saw The League of Extraordinary Gentlemen, well...that was heavily "steampunked," as was The Time Machine. Wikipedia has a pretty good explanation of Steampunk.
Here's an article by Richard Morgan about Steampunk.
I'm not sure just where I'll be going with my Steampunk fascination but I will admit I have some goggles. Goggles are the must-have accessory and can be worn around the neck, on the head, or on the face.
And I have a couple of semi-Victorian/military type jackets that I purchased a couple of years ago before I had heard of steampunk. I dug my riding boots and my Doc Martens out of the closet and am trying to remember where I put that actual Victorian shirt I have. Probably it's too small for me, but I could make a pattern....