I used to freak out, but last century I drove from Pittsburgh to Boston to visit family.
I packed for 2 weeks before the trip & my duffel bag was sitting in the living room behind the front door in anticipation of being loaded into the car. Well the day that we arrived in Mass at my parent's house as I was unloading the luggage, I discovered that I had forgotten to pack my duffel bag!
I had to buy enough clothes up there for the time we were there. I was not a happy camper. Nowdays I just let the adventure unfold...