Keys, which includes a bottle opener and a stupid engraved metal tag that I intend to keep as long as possible as I've had it since I was 8 (bought at a service station with money left over from a school trip...)
Wallet - cash, cards, photo-ID driving license, workplace door-swipe, stamps, etc
Phone (...communications, calendar, watch, gps/map, music, internet, entertainment, calculator, camera, torch, compass, starmap, phrasebook, guidebook, parked-car locator...)
.... er, what else do we tend to actually need, any more? Particularly "need badly enough to slightly restrict mobility and increase risk of theft whilst carrying it"?
I have a reputation for travelling heavy, but it's not true on an everyday basis. The back of the car is often full of anti-breakdown charms (a good quality jack, air pump and tyre sealant to ensure that I never so much as get a puncture much less a blowout, spare can of fuel to ensure I never forget to fill up, first aid kit and booklet to ward against injuries occurring, etc etc) but that's because getting stranded on the road can often badly ruin your day if not month.
Sometimes maybe a miniature screwdriver with a reversible end (philips or flat-head) or set of headphones as well, but not often. A short USB-A to micro-USB lead may be a common feature from now on seeing as my phone needs charging for about 6 hours out of every 24.
