This collection of items lives in an old rucksack along with old food wrappers, gloves and half-used bottles of suncream.
I find this list hard to believe. No old batteries? When I switched flight bags a year or so ago, I found enough of them to fill a plastic sandwich bag.
As far as what I do use: folding A4-ish kneeboard (charts to the left, notes to the right), iPad on a yoke mount. Pens, couple of torches/flashlights for night flying. Headset (Bose A20) of course. Pretty much nothing else that I take out for most flights. I carry a generic PoH for my plane in my flightbag (not sure why since there's one in the plane anyway), and the Pilots' Guide to California Airports (Pooley's equivalent) since it's nice to have on paper even though they stopped issuing paper updates a couple of years back. An E6B and aviation ruler for old times' sake. Check(que)book, you never know. I have a pulse oximeter but haven't been up far enough to need it in several years - not much use in the UK anyway. Spare key.
Nearly everything that the pilot supplies outfits try to sell you is unnecessary. Not to say I haven't fallen for quite a lot of it over the years.