Packing has always been a pretty daunting task for me. In the past I'd find myself with widely inappropriate clothes (because hey, maybe I'll need my little black dress while in Glacier National Park) and/or completely lacking essentials like enough underwear for the trip. Several years ago on that camping trip, I realized I was miserable because I didn't properly pack and had nothing I needed or wanted. So that's when I decided I needed to create a comprehensive travel checklist for every kind of trip I might take and have it on hand to tailor it to be my packing guide for any upcoming trip.
When I got home from that failure of a trip I created a running list of everything I could possible need for travel. I thought about what I would need for roadtrips, flying, extended vacations, traveling with my dogs, ski vacations, everything that typically do and then listed out everything I would possible want for each trip. I like to include everything since it can be deleted or crossed out for each trip but nice to think about all the same, like do I need to bring tweezers for a weekend trip? Probably not. But two weeks and I'd be looking like Friedo Kahlo. So I like to start big and whittle the list down.
The other key for me is mapping out my outfits for each day of the trip. I edit the document to reflect the days I'll be traveling and then build the outfit from the ground up; listing my shoes, socks, underwear, bra, top, bottom and jewelry. Although some things like shoes may be repeated I still find it helpful to check off each element and avoid not having the right undergarment or shoes for an outfit.
Here's my packing guide. Feel free to use it as a jumping off point for creating your own guide.