In late 1970s, I spent two months hitching and riding trains around Europe, just an external frame backpack and a sleeping bag. A few years ago, I spent 2.5 weeks in U.K. and Ireland, with an 18-liter backpack and a waist bag (a.k.a. fanny pack ), which made getting around a breeze especially at airports and on trains. It even allowed me to carry a notebook computer. As mentioned in TFA, merino wool and no cotton garments helps. The rain was a minor inconvenience, but I did have lodging where I could get things rinsed and dried out in my room. I did buy an umbrella but should have splurged on better quality, even if I would end up abandoning it.

Best packing advice I ever received: take half as many clothes, and twice as much money, as you think you'll need.