For a good while, I've been meaning to get a small cutting mat for the travelling toolbox.
Today I saw this for £5 and decided to bite the bullet - the knife is actually surprisingly good, too, with ten spare resharpenable blades, also. The fitted blade is spring-retractable by means of a "squeeze-clip" and there's a guard to prevent accidental activation.
The cutting mat is a good bit thicker than the usual variety - 200 x 130 mm.
Useful, if you're on the move - or pushed for space.