To overpack and have to literally sit on the suitcase to close it or underpack and not have everything you need? I had decided to dedicate half of my suitcase for clothes, so some had to be removed (which I may or may not regret now...).
Suitcase (clothes/shoes/cosmetics, chargers) & bag (books, wallet, water bottle)
I've yet to wear the blazer, but I'll wear it first thing when the weather permits (probably not anytime soon).