Over the years, and during many trips flying across the Atlantic, I have created for myself a travel checklist. It is the sum total of my need for preparedness - and I have expanded it to the point where I now travel without being nervous at all about any of my packing. I simply follow my checklist, cross things off as I pack - determining that some items are unnecessary this time, and others not - and I fly confidently across the world (well, the U.S. mostly, these days) knowing that I have everything I need.
Some items in the checklist bear witness to times when I forgot things, like obsessively checking before departure that I actually packed my toothbrush and toothpaste (because it's something you're very likely to use, very early that morning, before leaving).
It's also moved in recent years from being a flying-only checklist, to more of a pack-the-car checklist, but if you decide to use it, do it as you see fit. Feel free to expand it, modify it, or discard it. If you find it useful, try to update it for yourself as you travel with lessons learned. You will be thankful you did.