I always bring a car key, plus ID/cards/cash etc...not because I need the ID/cards/cash, but because car break ins are sadly not uncommon. The weight of all this is included in my list, but my list changes, sometimes subtly, sometimes not, for every trip, so I guesstimate a daily average for some items (medicine, toilet paper, tampons etc...). I don't usually bother with a cell phone as most (all??) of the places I hike are not within cell range.
Items no one else carries...umbrella sometimes, rain hat sometimes, glowstick, fingernail file, earplugs, etc...everything is itemised on my list, not because I'm anal about weights but because I print it out as a 'checklist' when packing to make sure I don't forget anything. I have this checklist laminated so I can check things off each trip, then rub the marks off with methanol to re-use the list.