This tour was our first experience with Europe and you will LOVE it! What are the ages in your party? That might make a difference in what some might suggest as activities.
Number one, IF you want to go up into the Eiffel Tower, you must book it ahead of time. I'm afraid with just a few weeks left if you haven't already done so, tickets will likely not be available. I know I got my tickets as soon as the booking window opened. It's worth a shot, though. Use the official website Official Eiffel Tower Tickets
I purchased a travel blow dryer that took up precious suitcase space. You won't need one as all of the hotels had something available either in the bathroom or at the front desk. You WILL need plug adapters. The generic Europe one will work. I purchased specific ones for Switzerland, Italy, and Germany/France. I also purchased a gizmo that plugged into our adapter that actually could take 3 plugs for our devices as well as 4 USB charging ports. I use this everywhere we travel as I have bulky dSLR batteries, small laptop, and of course other electronic devices.
Bus time is fun time! Your guide will utilize part of this time to acclimate you to the next city. You may have a little language lesson. You may get some history on the sites you are about to see. We made it a point to move around the bus on each leg of the trip. Give everyone a chance to sit up front. This way we got to know many of our tour members along the drive. Of course, if you are my husband, you used bus time as nap time ;) I couldn't sleep if I tried.....my eyes were peeled to the vistas!
If you are wine drinkers and plan to bring some back to the US, bring a Wine bottle bubble wrap. We had two of these and I can happily report both bottles of wine made it back in one piece in checked luggage!
I'm sure there's lots more. Don't go crazy bringing tons of shoes. Two sensible, comfortable, and well-broken in pairs are all you will need. Hubby only had the shoes on his feet! You will see more on this trip than you can ever imagine. I wish we had gotten the chance to go inside Notre Dame. That's a regret. We'll go back to Paris at some point.....we did enjoy climbing to the top of the dome in Florence as well as the Bell Tower. I would climb everything you can so you can really get a birds-eye view of the cities. This was something we did early on a free morning in Florence. We stayed 2 extra nights in Paris and I purchased the Paris Museum pass (48 hour one).....it was very helpful to not have to wait in ticket lines at Versailles (which we did after the tour), Orangerie, and the Orsay. The Orsay was our favorite museum in all of Paris! Hopefully you will arrive a day early in Haarlem, too. We didn't get the chance to visit St. Bavo in Haarlem since it was closed on that day....also, the Corrie ten Boom house in Haarlem is definitely worth a visit too!
Edited to add.....lots of memory cards for cameras if you are bringing something other than your cell phones. And at least one extra battery too!