I have at least one of everything in the office at all times.
Rule 1 - I could walk/cycle in stark naked after a week living on the streets/under a bush and be ready for a meeting with the MD in 15 mins
Rule 2 - I have an 'emergency pack' of socks, pants, shirt, trousers, tie, cuff links, and an aeroplane wash kit (shower gel, razor, micro towell, toothbrush etc) that lives in my locker at all times. In my desk I have a spare cycle lock, key and locker key.
Rule 3 - Finally I have a rule that I never take the 'last one' home in the case of shirts for example, so last Fridays worn shirt is better than no shirt at all
The way to build up the 'Office Emergency Kit' is next time a shirt, tie, shores, suit is on it last legs and ready to go to the great charity shop in the sky, keep it, and add to the office emergency kit.. If you dont have a locker, or your locker is not big enough there is always the file storage box that no one thinks twice about under your desk