Carryon roller suitcase + 26L Daypack

Regarding the CPAP machine, I recommend bringing it in the case it came with. It does not count towards your carry-on limit because it’s a medical device. Plus, the case will protect the machine and its supplies from damage. Enjoy your trip!

Hi JP, welcome to the forum! You’ve picked a good choice for your first trip to Europe.

Check whichever airlines you will be taking to see what their required dimensions are for both a carry on and the personal item, so you don’t encounter any disappointments at the airport.

My husband had a CPAP, and he would bring the half-section without the water, along with the hose. He placed it in his carry on because he didn’t want to deal with an extra bag during the trip. Test out whatever you’re considering by walking a few blocks outside in your neighborhood. : )

There’s a lot of posts about packing light (it’s a section in this forum) that can enable you to decide what works best for you to have sufficient room. I just bring a Cotopaxi 35L & an ORI crossbody purse for a month trip, but for ones like Christmas Markets I bring my 2-wheel carry on and a sturdy personal size backpack with a tiny purse inside it during the plane ride.

Have a great time!

This is a fairly standard set-up. Be sure to check with your airline to make sure your roller bag fits their specific carryon dimensions. Also consider the weight of the empty bag. You want one that weighs less than 6 pounds. Lots of bag recommendations on the Forum. The C-Pap, because it's a medical device, shouldn't count against your bag allowance, so if it came with a case, you can use that, or you can get a small bag (with a trolley sleeve) for it. Again, don't take my advice without checking with your airline.
A lot of RS tour members have what they call a "bus bag," usually a backpack or tote that they leave on the bus when not needed. A backpack isn't a great option for urban sightseeing for several reasons. Your crossbody bag is a better choice (though I worry about the word "mini"--you want it to hold your daily essentials (which, for me, includes a small water bottle). A lanyard for your phone is also recommended.
Be careful going too big with your "personal item" backpack, particularly if you intend to use this during your travels. One thing I learned from my Osprey 20L Daylite Plus is that a backpack should have a flat bottom so it can stand up on its own when you're loading or just need to set it down. The best way to shop for a backpack is to visit REI, where they have weighted bags you can put in the backpack while you walk around the store, take it on and off, set it down and pick it up. You'll know which weight to put in if you have assembled and weighed the things you intend to carry in your personal item. REI also has an excellent return policy, so if you pick the wrong one, you can easily return it.
A kitchen scale is a very useful tool for packing light, BTW. It makes choosing between two articles of clothing (or shoes!) that much easier. Weigh everything, including your packing cubes, some of which are surprisingly heavy. I use Lewis N Clark ElectroLight and FeatherLight compression cubes in a couple of sizes.
One more item I would strongly encourage is a packable tote or duffel bag. I usually bring along both the Peak Design packable tote (https://www.rei.com/product/241404/peak-design-packable-tote) and a Lewis N Clark packable duffel bag, which I don't think they make anymore (https://www.luggageonline.com/products/lewis-n-clark-electrolight-duffel?srsltid=AfmBOopw_36fmkg_SaPrynkC_4EjfWTMShX_7CkxbMwusKkZdT2UIsn3). The Peak Design bag is useful for the things I need on the plane, as well as to carry my purchases. The duffel is useful for laundry day (I am not sink washer), and I sometimes use it as my carryon if I check my roller bag on the way home (see above re: "purchases"). There are loads of packable totes (including Nanobag, which is probably the smallest), but I like having a zipper.

A 26L daypack is too large as a personal item for many airlines. I would suggest that you pack accordingly in case you have to gate check one of your bags..

That being said, I typically bring a 22” rollaboard, a 21L or 26L daypack, and a crossbody purse. I always check my rollaboard so the daypack serves as my carry on and the purse as my personal item. I find a 26L daypack too large for daily sightseeing but on a tour I will bring it on the bus. You can generally leave items on the bus when you stop for sightseeing. When sightseeing, I carry only the crossbody purse.

Thank you for all of the great suggestions!

Exciting that you're taking your first trip to Europe! You'll experience lots of new things, not all of them welcomed. To the point: if you're used to US domestic air travel, many carriers allow a carry-on size that's a little larger than most international carriers allow. For example, Southwest allows 24 in. x 16 x 10, but Air France is only 21.6 in. x 13.7 x 9.8. These sizes INCLUDE wheels and handles. The personal item limit is much smaller since it has to fit underneath the seat. On Air France, it's 16 in. x 12 x 6. Most 26L backpacks will be larger than that.

As mentioned, weight also matters, which is usually not the case domestically. For some it's as little as 7 kg (about 15 lbs) for BOTH items you carry on. The fare can also make a difference; Premium Economy and Business Class may have higher limits than basic economy.

And just to make us crazy, each airline sets its own limits, so if you travel on more than one airline for your trip (even partner airlines), you may be dealing with different rules.

This website gives you a good idea of what you're dealing with, but of course assume that it is not necessarily up to date -- always check your airline's website for the most accurate info.

https://upgradedpoints.com/travel/airlines/carry-on-luggage-size-chart/

Since this is your first RS tour, I'll add that carry-on is not "required," it is suggested. The only requirement is that you must handle your luggage yourself. This includeds carrying up stairs in hotels that don't have elevators. As light as possible is best, of course.

So many good ideas here, and do have a look at the 'packing' section, so much to learn. I actually looked at your tour, it's all or mostly by bus which is great.
I would start with the stuff ~ Put it all out on a table where you can leave it at least a few days, walk by and think about what you can leave out, not what you can add! Then cut back some more, if you want to have less stuff to carry. Of course you can take a bigger bag & even check it, but it's a question of what you really need and the schlepping from bus to hotel & back. Not all RS hotels have elevators, for example. Once you develop a packing list & consider what bag to take, you can post it under 'Packing' for feedback. Good luck!

My experience has been somewhat different than Laura’s. My 30L backpack has never been questioned as a personal item in my last dozen years of traveling in Europe or the US. But it does not fit easily underseat and leave any leg room should it need to be there for the whole flight. I think what is most important is to not pack any bag all the way full. It will be too heavy for comfort, Have fun!

Another bag to look at is the TomToc T69. It is 23 L expandable to 28L It measures 40 x 30 x 20 cm.

I just bought a new Ecohub backpack with the same measurements. But I am eyeing the Tomtoc.

Regarding the CPAP, most airlines will allow this as an addiional item if packed separately in its own bag. However, some airlines, especially the budget ones, require you to pre-register it.

Never pack anything of value that you can't afford to lose in your carry on. Just because a carry on meets the airline's requirements, if your flight is full, your bag may have to be gate checked. That opens the chance, although small, for either it being "lost" or the victim of theft.

Regarding the cross body bag, some airline will make you pack it away or it will be seen as a third bag and not allowed.