Congrats on booking your tour!
We did the DIY version of the BOE tour 5 years ago and just returned from 3 weeks in Italy. Here are my suggestions/responses to your questions.
I packed only my Rick Steve's Appenzell Daypack and a Tom Binh Small Cafe Bag. Both were perfectly sized for me. (I'm only 5ft 4 tall and the regular Rick's classic day bag was just a little oversized for my needs last trip.) I admit before the trip I was super stressed about spending so much money on one little TB bag but it's well made, waterproof, perfect size and had pockets and holders right where I needed them. The ability to strap all my items inside using the little leashes was AMAZING. I had my cell phone, camera, camera accessories, guidebook materials, breath mints, a small medical kit, Rick's emergency repair kit and other stuff all packed in there with room to spare! LOVE that bag and will take it with me everywhere now. Everything was tied down so it couldn't get pickpocketed, and so I didn't accidentally leave them behind!
The travel gadget we used the most was our cellphones. (T-mobile + Samsung) This probably would not be a necessity for a traveler who is on a guided tour, but it was helpful to navigate and to look for nearby pharmacies or grocery stores and to keep connected with family at home (who demanded daily photo updates of our journey lol). I also was able to document the restaurants and shops we visited by leaving reviews as we went along. After 3 weeks, I don't think I would have remembered all the names and locations without it!
Another favorite gadget would be our Sony RX100 cameras. I've owned the M1, Mark II, Mark III and now the Mark IV of this camera and It is (in my opinion) the perfect travel camera. It is as powerful as most huge SLR's but fits in your pocket. I bought the less expensive and easier to use M1 for my mother to use on the trip and she loved it.
The travel apps we used the most were:
Lifelock (it allows you to store copies of your credit cards, important documents securely on your cell phone and eliminates carrying paper copies).
Google Maps, TripAdvisor, Yelp and Foursquare. It was interesting to see how one rating site had such drastically different opinions about local restaurants. At the end of our 3-week trip I'd say Yelp and Google maps/google reviews are probably the most genuine and accurate...perhaps the travelers that use them are just a bit better traveled? Or have better taste? lol. The Trip Advisor reviews were great sometimes but usually just lead us to tourist traps. Foursquare was somewhere in the middle but did list some hole-in-the-wall-gem type restaurants that weren't even listed on TA so I give them credit for that.
Exsate Golden Hour - This photography app tells you when the "golden hour" is right after sunrise and before sunset...perfect lighting for photography. The app further lists the "blue hour" for night shots and the current moon phases. We used this almost daily to plan photo shooting times, or times to arrive at a scenic overlook (example Piazzale Michelangelo in Florence and top of the Victor Emmanuele monument in Rome).
Toilet Finder App --TMI alert -- I had my gall bladder removed a year ago, so when I need a bathroom... I need one NOW. This app was helpful finding free and paid bathrooms. Worked great in Italy so I'd assume it works well in other parts of Europe.
I just looked through my bag and the items I did NOT use were the following:
Flashlight (cell phone has one)
Alarm Clock (again, cell phone covered this need)
My big journal notebook (I spent 99% of my time out seeing stuff...not holed up writing about it!)
The assorted pens I brought, foolishly thinking I'd want to stay still long enough to sketch anything. lol
In regards to laundry, I much prefer paying a local service to do it. I want to spend as much time as possible exploring!
Bus rides are a great time to nap and recharge!