It's really only a guideline, but there are some durations set by the Govt that indicate how long each kind of food can last. This is where they get their best-before dates from, and they're often conservative.
Chances are a cured, well-packed ham will last a little longer than cut deli ham as it's not exposed to air like other foods, but you'd better plan to eat all of it the day you open it.
The Mt Eden foodtown is my favourite. The Quay St one may be a glitzy showboat of supermarkety extravagance, but I see through its gossamer-thin facade.
That said, the Grey Lynn one regularly has a bunch of $1 beers on special that are about to expire, and they even put the lot into a shopping trolley ready for me and my mates. We're often in a rush to drink as much as possible, so we appreciate their consideration.
----------------
I was editing some typos in the message above, and got the following:
Warning: Unknown(): php_network_getaddresses: getaddrinfo failed: Name or service not known in /global.php(429) : eval()'d code on line 1
Warning: Unknown(
http://www.nzboards.com/forums/inclu...ntend_init.php): failed to open stream: Success in /global.php(429) : eval()'d code on line 1
Fatal error: (null)(): Failed opening required 'http://www.nzboards.com/forums/includes/vbms_frontend_init.php' (include_path='.:/usr/lib/php:/usr/local/lib/php') in /home3/nzboards/public_html/forums/global.php(429) : eval()'d code on line 1