Next after your bike, passport and credit card, your smartphone will be the most valuable possession while touring. It will use quite a bit of battery during the day, so while biking I put mine into flight mode to last longer. During coffee breaks or lunch I sometimes charge it with my spare battery. The first thing I do when I arrive at my hotel room is to charge the phone by cable, so that I can use it when I go off for dinner in the evening. While away in the evening, I recharge my spare battery at the hotel. Quite a complicated setup, but it works.
Charging a phone abroad might be a bit complicated due to wall sockets and voltages. I suggest using a website to see if your phone charger needs an adapter to the wall sockets of your destination.
Above all I need Google Maps, without it I would be lost. Once in the french Alps my phone died in a heavy rainstorm. I ended up spending the whole next day going by bus back to Nice to buy a new one. So, the best choice is a phone which is water resistant. I once tried a holder for my phone that attaches to the handle bars, so I could use my phone as a GPS without having to bring it out of the jersey back pocket. Unfortunately it was quite hard to detach my phone from the holder when I wanted to use it as a camera, so these days I still keep my phone in the rear pocket of my bike jersey.
Laptops? No, leave them at home. Even a small sub 1 kg laptop or pad is too big to fit in the bags, and might be damaged by rain.
I do suggest bringing small earbuds, mostly for listening to music, pods or audio books in the evenings. Don’t use them while cycling – you need to hear cars coming up from behind!
Passing through the landscape on a bike gives you hundreds of great photo opportunities each day, and as a bicyclist you can stop almost anywhere for a snap. If your phone is in the back pocket of your bike jersey, you can be done in 10 seconds. But, phones aren’t as good cameras as real cameras, and your sweaty back pocket isn’t an ideal place for either of them. With my phone I have taken thousands of photos while touring, and looking at them today still gives me great joy. But these photos don’t scale well to something you’d want to put on the wall.
Finally, toiletries. For shampoo, bring one of these tiny bottles you get in hotels. They last long enough to get you to the next hotel with the same service. Small tube of toothpaste, smallest possible deodorant, you get the idea. Don’t bring a whole box of pills and tablets, half a dozen is enough. Hairdryer? No, I’m sorry, every day is going to be a bad hair day.