A final category - those items that are nice to have, although not necessary. I'll pack up everything else, and then see what space/weight is left.
Day
Perhaps a phone can no longer be considered a "comfort" item. I've forsaken the printed map for the convenience of bike mapping apps. And like most, it's hard to imagine spending a day unconnected to the world (although I fondly remember those times). In the past, I carried a digital camera thinking I'd rather it hit the ground (or disappear) rather than my phone. But the convenience, and great photos, that smartphones provide finally carried the day. Whatever you bring, make sure to carry the appropriate charger. I use a cheap, universal charger that has four USB adapters so that I can charge everything at once.
Evening
Campers debate the merits of packing a camp chair. For some, touring continues throughout the evening (pubs, downtown squares, nightlife), and the only time they're at the campsite is to sleep. My camping tends to be rustic and rural, and on many occasions, the campsite did not have picnic benches. I love my camp chair, a Thermarest Trekker chair. Simple, lightweight, and converts my sleeping pad into a comfortable (although low-sitting) chair. I also have a Thermarest Quadra chair, very nice and sits like a regular chair, although considerably heavier.
My headlight doubles as a flashlight, but I also pack a small dome light for reading during long fall/winter evenings. Mine has a solar recharger - which works great if I remember to strap it to the outside of the panniers before starting the day's ride. And it's sunny. Finally, a tablet and/or book to make you feel like a real tourist.