I am a recovering over-packer.
I've been working hard on doing some planning to reduce what I need to take, and even purchased some items to enable this (for example, I purchased plain, but leather work shoes that are acceptable on the shop floor or in the office). Or, I pack lots of under things, and only a few over-things. Under things being generally smaller and lighter. So, I could change my undershirt and socks every day, but maybe wear the same shirt twice. I only brought 2 sweaters, and made sure all the tops went with both, so if one was in the laundry I wasn't locked down.
I also work out laundry in advance if possible. I've had some 3 week long trips and trying to bring all clean clothes to wear a different outfit every day just wasn't going to be easy to do.
I agree though, for a car trip, I'm much more liberal, though one time I visited my cousin with workout gear and a yoga mat, hiking clothes, regular day clothes, a sundress for shopping, and really nice evening wear in case we went out for fancy dinner...and then wore only the sundresses, and the rest of it I fretted if it would get stolen while being parked on the street because it didn't all fit in her tiny apartment!