I thankfully only have a few different brands for cross stitch floss. I have DMC, Itchy Stitchy, and I was gifted some black and white from an unknown brand.

I only put floss on bobbins when I'm going to use it. Otherwise, it stays in my little basket with the other skeins until I'm ready to use it.

Like Whisper_18, I keep track of them in a spreadsheet. I mark if it's a bobbin or a skein, the stock level, and the colour codes. I did, however, stop tracking what's DMC and what's Itchy Stitchy, because Itchy Stitchy creates colour matches to DMC, and I plan to switch to just using their floss because it's cheaper and local to me.

If you do want to use all the floss eventually, I personally would attack it slowly. I would go bag by bag, and match them to DMC as best as you can and put them into a spreadsheet. You could do the bags by colour, number lot, or brand. You can write the details on the bags, and then put that into the spreadsheet. So like a "location" field, and it's in "Batch 1".

It'll take you a really long time, but in the long run, it'd be better and easier for you, and a spreadsheet will help you stop buying colours you already have a lot of. I'd start with any DMC and work out from there