The real danger is, when you get to work, shower, and head over to get dressed, you realize that you packed a mostly black shirt, black socks, black shoes, black belt, and navy blue pants. :O Talk an ugly situation and nowhere to turn.
yes over the 4 years of full time commuting, i have forgotten a few things:
* twice forgotten my shoes and had to work all day in my cycling shoes
* twice forgot my change of underwear (just a few weeks ago), once wearing my semi-sweaty bike underwear and once going sans
* a few times forgetting my undershirt but that's not so bad
* twice forgetting my outer shirt - once i had a spare in my desk and the other i wore a t-shirt all day
thankfully, i've never forgotten my pants (uh, having to work in cycling tights or bike shorts all day would not be fun), and since i dress casual matching isn't much of an issue (i wear jeans mostly)
i try to keep s spare shirt in my desk, but actually at the moment i don't... hmm need to remember that! actually maybe i should add underwear to the backup-store too...