We all do it. A few days before (or the day before if you like to procrastinate like me) a vacation, you sit down with a piece of paper and write out a list of everything you need to pack for your trip - toiletries, clothing, food, entertainment, extras. Sometimes writing the list takes longer than packing your stuff. After doing this a handful of times, I thought, "Why not type this up in a Word document and that way I can just edit and print and be done in a minute?" So I did. I thought of everything that we would normally pack for trips and made a column for each person or category. Then when we go to pack, I don't spend time thinking of what needs to be packed or worse, forget something because I couldn't think of it. It has changed over the years (ie diapers for Luke became underwear for Luke, bottles became sippy cups, etc), but overall the general list is pretty usable. We just hand write a few of the extra things we might need (ie food for meals, specific snacks we want, movies we want to bring, etc). Easy breezy.
If you would like to see my packing list, I would be happy to email it as a Word document attachment. Just e-mail me at firstname.lastname@example.org.