I probably would come value most what I didn't have when I needed it, whether or not I had ever used it prior to that time or ever used it after (like a spare inner tube). However, the one thing that I take every day and use every day is the Ortlieb waterproof messenger backpack. I'm an "on the body" guy instead of an "on the bike" guy because I can go this way on the main bike or on the backup bike.