Common practice in the UK is to view the association of the box and the contents as extremely important. This is recorded when the item is accessioned and both parts (box and contents) would be given the same number with a .suffix to show the relationship – e.g. the number might be 2012.003.1 for the contents and 2012.003.2 for the box.
Wherever possible the contents are kept in the box to maintain the association. Where this is not possible (e.g. the contents are placed on display or require different storage conditions from the packaging) the items are kept separate, and their two locations re recorded in the society’s documentation. Great care must be taken to make sure the numbers are clearly and unmistakably written on, or attached securely to, all items. Hope this helps. As with all documentation – loss of the information is as severe as loss of the actual object and prevention is much easier than cure !