Wheels on luggage. This is so obvious, but it didn't existing until 1970 when Macy's began selling the US Citation Roll-away or simply “Rolling Luggage” marketed as "The luggage that glides". I imagine this invention pretty much doomed the Luggage Porter industry.
Check back for more examples of things that were not obvious until they were.
@MattWalshBlog Your Honor, I’m a big fan and I listen almost every day. Your judgement is valid for the two movies you mentioned, but there are other great Christmas movies. I humbly submit that White Christmas, Christmas Vacation, Home Alone and Elf deserve recognition.