Despite mentioning it months ago, I still have not got myself organized when it comes to looking after the growing collection of SD cards with different versions of Raspberry Pi software on them. It doesn't help that many of them are outwardly identical, either.
Having failed to buy any little stickers, I have now decided that it's more important that I know what's on the cards than that they are pretty, so I am taking a two-fold approach.
The first step is something I should have done ages ago. I am putting a small file "contents.txt" at the root of each card with some notes as to what OS is on the card, versions, dates, installed software, what it is used for and so on. This is such a simple solution that I feel a complete idiot for not thinking of it earlier. Even my bare-metal OS cards have the standard boot file system with cmdline.txt, config.txt and kernel.img etc. Adding an extra file is no problem at all.
The second step is just to help with identifying cards without plugging them into a computer. I have found a sheet of printable address labels, so I'm just going to snip off some little rectangles of "sticker", write a number on each one, and stick it to an SD card. For basic telling-the-difference that should be enough, but I also plan to keep a little index on a piece of card.
When added together, these steps should finally help me work out what is on each card, and (hopefully) reduce the temptation to just format a new card whenever I get confused!