But in today's world of flight, you can't use just any locks on your bags while flying, they need to be the type that TSA can open as needed (without destroying the lock). These approved locks are designated by the red diamond symbol you see on the upper right corner of the photo here.
If you have other locks, you could throw a couple inside your suitcase to use in the hotel rooms.
And speaking of hotels, most in Europe do NOT provided washcloths (aka 'flannels'). So, maybe you want to throw an old one in your suitcase (and toss it at the end of the trip to have *that* much more space for souvenirs), or a mesh sponge that squishes down to just about nothing.
One last thing for today: pilgrims, please check your email for a message I sent yesterday about purchasing Euros. I've already received several checks, thanks!