Common in professional kitchens, painter's tape and a good marker should be a part of a home kitchen as well. It works best on deli cups but it can be used on most surfaces. Better, it can be removed from them as well, without leaving stickiness behind. (Photo by donna, thanks sweetheart!)
I store a lot of stock in a basement freezer and every container gets marked and dated. Don't even think you'll remember what that stuff is under all that frost. Don't think you're going to remember how many yolks were left over from making angel food cake.
I first saw blue painter's tape at The French Laundry years ago. Thomas Keller's restaurants now use green painter's tape because, I believe, it's even cleaner when removed than the blue stuff (more expensive too). I like blue just fine, and while French Laundry and per se cut their tape at perfect right angles, I'm a tearer.
No matter how you cut it, painter's tape is an important tool, keeping you organized and preventing waste. Get rid of that avocado slicer and egg separator cluttering your kitchen drawer and put a roll of tape in there instead. Find a spot to keep a Sharpie, then keep it there, and put it back when you're done so you always know where it is.
Being organized in the kitchen makes cooking faster and easier. (And btw, if you find yourself with a similar deli full of yolks, it's time to make vanilla sauce.) All comments on what you use to stay organized in the kitchen are welcome!