If you start each filename with an alphanumeric title, it will be easier to keep everything organized in the long run. I guess you don't need to use a letter, but it does help me remember when certain ideas were initially started.

When a mix sounds solid enough that I may want to reference it later -- in case I fuck up the beat, which I likely will -- I export a .wav file of it and then continue working under a new .flp file. This is also beneficial for playing through a long list of mixes and trying to find something that I'm in the mood to work on. I've found that the more regularly I scroll through the list of .wav files, the easier it becomes to remember roughly where particular tracks are saved.

B243 Untitled 001.flp

B243 Untitled 002.flp

B243 Untitled 002.wav

B243 Untitled 003.flp

B243 Untitled 003.wav

etc..

B243 Some Corny Title With The Word Life In It Cause Rappers Love That Shit (final).flp

B243 Some Corny Title With The Word Life In It Cause Rappers Love That Shit (final).wav

I also have a document listing each beat's alphanumeric title, the potential\final title, current BPM, current key and any other notes I may need in the future. Keeping the document updated though is probably the most difficult part of staying organized.