Since this is a pretty standard trip, most of the places are going to be pretty bag friendly. I wouldn't bring a ton (lots of hotels have washing machines too), and would definitely recommend a backpack or something with wheels. Don't make the mistake of bringing something you're not comfortable carrying up and down long flights of stairs. You will run into a lot of these getting on and off trains, so if your biceps are tiny, only pack whatever you can lift (preferably less). Also, bring a lightweight duffel bag (or you can buy one) for the optional shopping you can do at the end of your trip.