From a NCL gold member on many of her cruises, one thing that I would add to the final charges is (not counting the casino losses / or, winnings )
for all those bingo games that people play, usually on sea days in the lounge and even those "instant" game pieces before the shows in the main theater -

We've seen couples screamed with the final bills in hand, lined up at the reception desk, trying to understand why it was so much (not unusual to be as much as $400 or $500, or higher after 3 days of morning & afternoon game sessions, with multiple games played on those digital scorecard boards at $40 or more per session x 2 people) It's easy to just sign & approve the charges as all they need is your room key card to post it to the Onboard Account.

Last minute or gift items ("on sale") purchased in the gift shops or the mega ship's "shopping mall" can also add up quickly, especially if you forgotten a swimsuit, need a pair of shorts or other things. Plus, there will be those daily special sales ("designer" watches & jewelry, duty-free items) and last but not least - professionally photos/packages as taken onboard. And, that's with a full bypast of the art gallery & its auction with promises of free shipping & no taxes)

Some cruisers are known to stop at the desk midway thru the trip to check on their running balance on the account, to avoid surprises and to put a curb on more charges being "signed" off for being posted to the cabin.