Full disclosure, I travel almost exclusively carryon only, even for 2-3 wk trips to Europe.
Travel as light as you can. European hotel rooms tend to be smaller. Even with ABD shlepping your bags for you, you won't have a lot of space to put stuff.
Consider AirTags for any checked luggage.
In your carryon, bring a spare change of clothes, all meds you need, and any other item you can't live without or replace easily.
Things I always travel with:
compression packing cubes
multi-country adaptor with USB ports
a small tray to keep next to the bed for glasses, chapstick, earrings, etc - it packs flat and snaps on the corners
small bars of soap (Europe has gone to liquid soap in the shower, not my thing)
laundry soap sheets (just learned the trick of bringing a dry bag to wash in, instead of the sink)
pashmina scarf - works as a blanket on the plane, scarf, head cover for churches, hood in the rain
my cross body Pac-safe bright orange purse
water bottle
a few zip lock baggies (small and large), garbage bag, plastic grocery bags
baby wipes, travel size kleenex
comfortable shoes - way more important than those cute little flats for a long day of touring
photocopy of my passport
a small backpack to carry umbrella, water bottle, snacks, small purchases, my kindle for the bus ride, hat
I wear my cross-body purse, zipper to the inside (and locked depending on the location) and my backpack. I totally look like a tourist, but that way my valuables are safe and I can carry the other stuff.
Bring clothes you can mix and match. My travel wardrobe is different than my daily wardrobe. It's mostly technical fabrics, dark pants and dark solid color shirts. They don't show dirt as much, don't wrinkle, and dry quickly if hand washed.
You just won't need much cash, especially since you won't be arranging your own tours. Money belts/neck bags are nice, but you won't need to put much in them. Any cash you need, you can stop by an ATM which are almost more ubiquitous than in the US.
