I would expect any breakdown like this on a large ship to be resolved relatively quickly, either by emergency repairs or by towing to a port as has now been done.
I presume that a standby generator, located away from the main engines was available for emergency lighting and the public address system. Some reports speak of cabin doors being left open "to admit light from the corridoor emergency lighting" I doubt that batteries would last that long.

I would agree that water purification tablets, flashlights and a small stash of non perishable foods would be sensible.
Bit suprised that no one suggested glowsticks, these could be usefull.

I dont think that an emergency of this type would be allowed to carry on for long, with hundreds on board.
Supplies can be air dropped, as was done, or persons evacuated by air, by lifeboat. As a last resort the stricken vessel could be towed by a warship.

If the ship sinks, or suffers fire throughout, then personal supplies wont help that much, though flashlights are useful.
The lifeboats should be properly equiped, and rescue relatively quick.