So, this little hack can be used for just about anything, but one of the most useful ways to use it is to cover your paint tray in aluminum foil. This will allow you to easily remove any leftover paint after you're finished and it leaves you with a clean tray. No more having to scrub away any paint or even worse, just leaving the dried-up paint in the tray.
If you're low on dropcloth, you can also just use aluminum foil on the floor to soak up paint splatters that might try to find their way to your hardwood, tiles, or carpet. Easy!