Carry on and backpack?

That is what we travel with indefinitely. I carry a small day pack, not a big backpack, as it needs to fit under the seat.

Look at your airline's carry on baggage allowance and make sure your bags conform.

There is quite a bit of variability from one airline to another, that a general answer here may or may not be accurate, for your airline

If you are wondering if RS allows a 21" and a backpack, they don't really restrict you. There's plenty of room in the bus. You can bring what you can carry. RS doesn't strictly measure your bag. It is just a suggestion. And you need to be able to manage whatever you bring.

If you are wondering about what you can bring on the flight, you need to check your airline. Regardless, you can always check your bag if it is larger than the carryon measurements.

I am looking for information on luggage allowance for carry ons.

Is each person allowed to take a 21" suitcase as a carry on as well as a backpack?

Maybe. Maybe not. And of course it depends on what you define as "a backpack"... Every airline is different. Look on your airline's website for their allowances. There are also other variables: flying coach? "basic economy" (sic). etc.

If flying on more than one airline, be sure you figure for the most restrictive flight you will be on. Note that European airlines, and especially "low cost carriers" often (usually) have very tight restrictions - sometimes shockingly so. Read the airline website details carefully and take them seriously.

Note that European airlines, and especially "low cost carriers" often (usually) have very tight restrictions - sometimes shockingly so.

I wouldn't describe them as shocking, they're tight for a reason. Aircraft overhead bins were never designed to accommodate the volume of luggage people are now bringing on board and there's no justification to bring a suitcase and a backpack as carry on luggage. I'm fed up of my flight being delayed because cabin crew are rushing around trying to find space to store luggage, fed up of having my single bag squashed and shoved around to squeeze other peoples luggage in (I have a small duffle bag containing my valuable electronics) all because some people can't be bothered to check in their luggage because it involves waiting for it in arrivals.

No-one needs a suitcase full of stuff whilst they're in the air, there's no reason why it can't be checked in and a small bag containing personal items for use on the plane or valuables.

I hear what JC is saying about the overhead bins being crowded but I just travel with a carry-on because I've had to deal with lost luggage on a trip and I've learned to pack very light. Something that I've found that works for my wife and myself is that we each have a carry-on bag that measures 21x14x9 inches, this has always been acceptable on international flights to and from the USA to Europe, next we each have a jacket from Scottevest that has multiple pockets on the inside and the sleeves detach to make a vest. We use the jackets for all the things that we will need during the flight, my wife doesn't even take a purse because she likes the jacket/vest better.

After traveling in Europe over the last 10 years we've refined our gear to take only what we need, if your daughters take a regulation sized carry-on then their backpacks need to be small day packs like the Civita on the RS website.

Your going to have a great time on the RS tour, how wonderful to share it with your daughters!

Don't check a bag. When the airlines lose luggage it's bad enough if it's yours, let alone your family. And, you'll be moving quite a bit on this tour, so if it does not catch up with you right away, it may not. Check your airlines requirements. We've managed 7 RS tours with 21" spinners and a small bag that sit's on top of the suitcase when rolling it. Inside we pack RS Civita daypacks which compress to nothing and hold all we need while touring. While RS does not restrict what you carry, they strongly suggest packing light, minimizing your luggage size, as you will be carrying/rolling it many times. We always see fellow tour members who ignore this and struggle with overweight/oversize bags. And on 3 of our 7 tours there were folks who checked bags and had them lost. One poor gal in Greece did not see her luggage for a week and she had liltle else but the clothes she wore on the plane!

As Wray noted, I think the OP is asking about limitations on the RS tour. swetrich, if thats the case, its not a limitation, its a strong recommendation that you take only carry-on sized luggage on the tour. It's because you will be responsible for carrying your bags from the bus, down the street, up the stairs, etc. No porters. The more you take, the greater possibility you will slow the group down.

That being said, yes a daypack is a good thing to have with you on the bus, while your main bag goes in the storage compartment. You'll want to have snacks, books, meds, etc., with you on the bus. On our three RS tours some people have traveled with very large bags anyway, although most followed the guidance with carryon-sized bags. Or, like me, some end up with an extra bag full of souvenirs and dirty clothes. As long as you can manage your own bags, you won't get in trouble.

Really would help if you indicated the size of the "backpack." A backpack could be anything from a book bag to an external frame backpack. So what size is it?

Just to add to the above...
First, if flying on different airlines - follow the most restrictive luggage protocol.
Two options to consider:
1) carry-on suitcase and a backpack or other bag (i.e. Purse, tote bag, etc. that is 22 liters or LESS) as a personal item/ underseat bag.
2). Larger travel backpack (about 35 - 45 liters) as the carry-on bag for overhead bin and another bag for flight bag/underseat bag.
Keep the personal/underseat bag small - under 22 liters. 15 liters is a good size. You can use a volume converter online to help with dimensions.
Good sources for luggage: Eagle Creek.com, ebags.com, LL Bean, Eddie Bauer. Eagle creek and Ebags are my favorites. Packing cubes can help a lot. My favorites are ebags Classic cubes and eagle creek basic cubes and folders.

If the backpack can fit (or be “squashed”) under the seat in front of you, you’re probably okay. 1, don’t try to use a large travel backpack as the personal item. It won’t fit. 2, don’t fill the pack too full—see “squashing” point above.

One more thing to add. Once you know the carry-on rules (# items & dimensions) for each airline you are traveling, go to SeatGuru and check the airline seats you are booked into. Many long-haul aircraft have significant amounts of under-seat space taken up by equipment boxes (entertainment systems, HVAC, etc.). That daypack may fit under the seat in 23D but not under the seat in 23A or 23F.

Also, don't forget to consider the trains and buses you will be using in country. You have to be able to schlep and secure all that luggage when moving around for those 2 weeks.

I would spend an evening before you leave investigating laundry facilities along your route and then cutting your packing down to the minimum.

And to further complicate this, some airlines have weight limits on carry-on as well -- just flew home on Lufthansa and their stated limit is 8kg (about 17 pounds) although I did not see anyone weighing cabin bags.