While intended for use as a drawer organizer, I found the Pipishell (funny name I know) Bamboo Organizer to the perfect part organizer tray for building sets. As you may have seen in many of my videos, I use this organizer for nearly every set I build and it makes my life SO much easier.

The organizer features expandable side compartments which are super useful for loooong parts and some customizable compartments in the center. By default there are three horizontal separators which are fixed in place and cannot be moved however by removing the few small staples you can gain extra customization to the internal layout(just be careful not to hurt yourself by doing this).

If you build a lot of sets like I do, I would highly recommend picking up a part separator like this one; it is a huge improvement compared to dumping your parts all over the table and makes things easy to move or put away if you need to take a break.