This.

Flying SJU-CLT-YOW on US earlier this year right before they left Star Alliance, had my winter coat in my checked baggage (luckily I had one change of clothes in my carry on backpack, but a spare t-shirt only gets you so far in winter). My flight to YOW got cancelled, which started a chain reaction that left me waiting in CLT for a couple of days with temperatures below freezing until I could get out on AC, and then stranded again overnight in YYZ on the day that the airport effectively shut down because it was "too cold".

To US' credit, they actually got my luggage to YOW a day before AC got me there. Of course, that wasn't much consolation when I was stuck in YYZ on the coldest day of the year without proper winter clothing. From now on when travelling in winter, carry on includes my winter coat and a change of clothes at a minimum.