What you might want to do is make up a master packing list for travel. I have one on Google Docs. This is your template. Put everything on it you might take on a trip. This list is constantly updated and revised after each trip to see what I may not want to take any longer or if I find something that is better than I have now.
To make your own packing lists, peruse numerous ones on the web. Don't just use one person's list as they may not take something you would. Just Google "packing lists" and you will get tons of examples.
When I am getting ready for a trip, I make a copy of the packing list and paste it into a new document with the title of the trip. Then I start going down the list crossing off anything I won't take. (example--thermal underwear for a trip to the Mediterranean.) I also ask myself if I really need it or can I get it wherever I am going should I need it.
This also helps to make sure I don't forget anything. (And since it's in Google Docs I always have it with me.)
Once that it done, I start to think of how i will pack it. I go so far, and I know this may sound ridiculous, but I get out a sheet of graph paper. I then mark off the dimensions of the bag using each box as an inch. Since I use packing cubes, pouches and sacs, I can play Tetris and figure out how to best pack it. I do this for each bag since they all pack differently. (And of course, I've already decided what goes in each cube/pouch/sac--see below.)
If you really want to be obsessive about this, you can measure and weigh every item on your packing list so you know how it will affect your packing.
To be extra, extra neurotic about it, you could make a separate list of packing aids and under each one put what will be going in it.
Yes.....I do this. I have a lot of time on my hands. Hey, I'm retired and it beats playing shuffleboard.