My original intent was to exclude things you carry for "normal" unexpected events - so I wasn't really thinking of first aid kits or 10-essentials as "backup" gear. It was intended more as "what are you worried about breaking so you carry two (or more)?"

However, I think the items you've all mentioned certainly add to the relevance of the discussion, since they can be creatively used to overcome the failure of some of the other items. (For example, iodine in a first aid kit to purify water.)