Lots of bank notes and coins will need changing, since they have QEII's face on them. Not just in the UK, either - also in other Commonwealth countries (e.g. Canada, Australia).
You make that sound onerous
, when it really isn't. In the UK at least, current notes and coins will remain legal tender for as long as they are in natural circulation. There's a natural flow of currency being officially destroyed and replaced with new currency from the Royal Mint, and all that will happen is the new stuff will bear the King's head rather than the Queen's. I remember having old shilling coins with the old King's head on it, right up to the point they changed the 5p piece to the small thing it is today (1990, iirc). The shilling became equivalent to the decimalised 5p, so shilling coins were legal tender as 5p, even if they were so old as to be pre 1952.
The same for all our stamps. They remain legal tender pretty much for ever, irrespective of which monarch's noggin is on it.
Public post boxes in Britain also apparently have EIIR (Elizabeth II Regina) on them, so they'll all need changing eventually.
Only in the process of natural replacement, or for brand new post boxes go up. I don't think they'll replace the existing ones just because of the change in monarch.
There will be a reconsideration of various Royal warrants (i.e. special recognition of companies that supply things to the monarch, whether it be cutlery, clocks, or other goods).
Certain badges (such as those the police wear) that display the monarch's cypher will need to be updated, sure. And the King may change some of the warrants, but not necessarily so, and likely over time rather.
Don't get me wrong, there are many things that will need to be updated to reflect the change in Monarch, but unless it specifically needs to reflect the
current monarch, the change will likely only be introduced gradually as things are naturally replaced. I.e. there is unlikely to be a significant effort to replace things like coins/notes, stamps, post-boxes etc.
And yes (before saint asks!), the QE2 ship (retired) will still be called the QE2, even if it is now a floating hotel.
Meanwhile, the other members of the royal family will go through some adjustment to official titles, Dukedoms and the like.
William and Kate automatically become the Duke and Duchess of Cornwall, taking over from the now King and Queen Consort. The title Prince of Wales is apparently not an automatic one, but will presumably be passed to Prince William in due course. The other titles, yeah, things will change and be passed around, not that the specific titles will mean much to many people.