Whenever I start packing for a trip (usually several hours beforehand), I spend most of my time agonizing over what clothes to bring. It takes me a while to think about where I am going, what the demands are, what the climate is like, and so forth. It’s a bit silly that I can’t seem to do this any faster.
And, usually once I get there, I realize that I forgot something. Most often I can live without it, but sometimes I’ve had to make quick purchases. Oops.