I only keep spare writing utensils and notebooks in my other bags, my other stuff (lunch bag, 2 first aid kits) is in small bags and gets transferred when needed. I keep most of my edc stuff on me instead of having it riding in a bag, so that makes for less stuff to transfer. Also, I mostly stick to one bag except for when I need more gear and thus have to grab my larger bag. As to carrying doubles of an item, I mostly do not. I already have one, why do I need another that is the exact same thing? As to carrying multiples of the same type of item, I often do as some items in the same type are better at some things than others. For example, I often carry two 1xAAA flashlights. So, if I lose one, kill a battery, or more likely leave my main light at home by accident, I still have my spare on my keys. Another example is when I carry knives, I often carry one serrated blade and one plain edge. Also, one is generally smaller and one is larger. I often carry two writing implements, a mech pencil and a multi-pen. In all three cases, the two similar items compliment each other and work well to back each other up.