Most cafes, bars and restaurants have electricity. Just charge your devices and even your power pack as you go along.
One of the most useful ‘must have’ things I bought years ago - and has never stopped being handy - is a very basic Continental three-way mains plug splitter. It takes up no room and weighs next to nothing. Pop into any half decent DIY or similar store next time you are abroad and pick one up.
The other great thing I also bought was several long, well made, USB leads. Why? Because the bloody wall sockets are often not where you need them, made more difficult when your USB lead is only 9” long.
One last ‘great buy’? Most charging blocks (the thing you put your camera battery into) use a standard figure of eight mains lead, terminated with a bloody great UK plug, which means you need an adaptor, too. I bought a Continental figure of eight lead, enabling me to leave the UK one - and its adaptor - at home.
PS Wiring a 12 volt feed to a motorbike is really easy; there are lots of threads and posts on how to do it.