The one thing I don't ever want to see again is the PCs going into business and commerce.
This happened to me once, where a rich and successful party decided to go into business. They left a few PCs behind to run it full-time (which worked out as a great place to park some characters of players who left the game around then) while the main group kept adventuring, which was fine for a while.
Problem was, before long every time they got back to town they wanted fairly in-depth updates on how their business - which later became multiple and many businesses - were doing, and what the PC investors had coming to them as dividends, and what businesses needed help, and where they could expand next.....
Never again.