I think packing for any domestic destination is far easier than packing for an overseas trip. I mean, if you are anywhere in the USA and realize you've forgotten something, it isn't usually a disaster.... we have shops galore all over the country and one can pick up just about anything from coast to coast.
What I found tough was packing for international destinations... simply the process of learning the differences was a little daunting. For instance, electrical outlets are different in Europe and one needs to either pack an adapter or buy a European curling iron once you've arrived. Plus the issues of currency and language. Fortunately, there are lots of great resources available to the would-be traveler and plenty of well-traveled people around who can advise.
I used to fly quite often when I was young. Don't even get me started on the topic of Lost Luggage!

Once, an airline lost both my big bag AND my guitar. I eventually got it all back again, but my bag ended up first in a warehouse in Chicago and my guitar made a round trip to the Orient!
But meanwhile, there I was hundreds of miles from home without so much as a toothbrush on me! Fortunately, the airline took good care of me, putting me up in a hotel (they'd also messed up my connecting flight), letting me shop in the hotel's shop for anything I needed.
Still, it was a lesson learned and ever after that, I always carried really important items in a small "carry on" bag (giant purse) and did not pack anything in a suitcase I couldn't really do without.