For anyone working in retail or otherwise having to open a lot of boxes etc, these are the most useful knives ever invented. Small and thin to keep in a pocket (only 4mm thick) but razor sharp and the blade retracts.
http://cgi.ebay.co.uk/Set-of-8-Olfa-...d=p3286.c0.m14
They also do a magnetic version, a bit bulkier, but sticks to your metal cabinets or the metal supports in racking etc. so you won't lose it. Some stationers are cheaper than Ebay, google "olfa knife".
Handy knives
