Making Wall Touch-Up Markers out of Leftover Paint
Good for latex paint.
Make markers by freezing some leftover paint in an ice cube tray (easiest to use a silicone one from the “Dollar” store).
Either place the tray in a plastic bag or remove and refreeze the cubes (so that the surfaces don’t stick) on a tray, then pop them into a sealable plastic bag.
Use a cube like a marker or crayon to touch up marks on the walls or spots that you are repairing.