We take most of our major fun trips during shoulder season: February/March and September/October. This means that it's not usually super cold wherever we're going, but also I'm from Texas, so I tend to think it's cold whenever it's below 50 degrees.
Andy will say, "It's not even cold!"
To which I reply, "Maybe it's not cold, but I am cold."
I bought this packable down jacket a few years ago when we went to Italy, and it's been a complete life-saver ever since. If I'm ever packing and wonder if I should take it or not, I just toss it into my carry-on, smush, and go. I'm always glad I brought it!
Also, this particular jacket has two really deep inner pockets which I pack like a squirrel rather than carry a purse. In cities, I throw my phone, chapstick and gum into my pockets and I'm ready to roll. Hiking in Cinque Terre, I bought tiny little pottery bowls In Vernazza and carried them back in my pockets.
I was fortunate enough to find my jacket at Costco for around $30. If you see it come into Costco in the fall, you know what your mission must be: snatch it up right now because it won't be there tomorrow!