I have a "master" install checklist procedure, which I use when setting up or rebuilding one of my machines (it happens more often than you think).
In that checklist, I have the serial numbers or install keys for (nearly) all of my programs.
I also have the registration keys for AHP and the plugins in that file. It makes the process a lot simpler to have it all in the same place.
In that file, I also have the steps to implement all of the "tweaks" that I like to have (file sharing settings, time sync stuff, other registry tweaks) so that I don't have to try and remember how I got something to work the way I like.
Given my ADHD, extreme organization is the only way for me to make sure things don't get lost. Some people say I'm too "anal" about things like that. Only years later, after taking an ITIL course, did I find out that this is not "anal", but rather "Configuration Management"