Bill
In the winter I've been known to carry 4 pairs of gloves - sleeping, xcskiing, goretex shells and heavy warm insulated goretex gloves. Often 4 BIC lighters cause I end up spreading them around and can't find one when I need it. A closed cell pad under my airmattress is definitely backup (or rather spare stuff thats not really probably needed but gets used.)

By your definition my entire first aid kit, photon light, spare batteries, etc, are backup because they never get used but are carried anyhow.
Jim

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These are my own opinions based on wisdom earned through many wrong decisions. Your mileage may vary.