Another common problem is pet-hobby packing.
Some people, for example, are gadget geeks so they have two SAK and two Multi-Tools in their kit. In 32 years of hiking, survival training and experimentation, and training I have never ONCE used or needed or wanted a multitool.
Some people, for example, are tech geeks so they have a pair of solar chargers to prep batteries for gear they don't need. The only battery powered device needed is a flashlight. I don't even advocate battery powered radios in EXTENSIVE LONG TERM kits. Get a wind up.