I would recommend going to your local outdoor outfitter store and checking out the different backpacks. A good store will have many choices in various sizes.

My favourite store is Mountain Equipment Co-op (MEC), but I'm in Canada. I believe the equivalent store in the US is REI (assuming your in the US).

At MEC daypacks range in size from 15 to 35 litre capacity. That's a pretty big range so it's best to check them out in person and see how much the different sizes hold. Also, you'll want to make sure that it's comfortable to carry.

Here's a link to the MEC daypacks catalogue where you can see there's a lot of choices out there:

http://www.mec.ca/Products/product_listing.jsp?FOLDER%3C%3Efolder_id=2534374302699687

I would check your airline will allow two pieces of carry on. In any case a backpack does not meet the description of a personal item which is what the second carry-on piece is supposed to be.

hetismij actually i was going to check the roller carryon for the flight. i am taking some trains during the 3 weeks so I thought if I needed two pieices - one roller and back back would be easiest.

Yes - I will visit a local Sports Authority and Dicks sporting good store here in FL. Seeing them and trying them on is best.

I had no idea how important it is to have a backpack properly fitted to your body until we decided to do a walking safari. It's a bit like buying a sneaker - you'll try on 10+ before you get one that feels Just Right. I will say that you should still be able to find decent comfort without a frame, but it won't be flimsy enough to fold up, so don't imagine you could roll it up and put it in your other luggage if you got tired of it.

Also, ShelliDawn is correct about getting to an outfitter, not just a generalized sporting goods store. You'll need the help of a knowlegible sales person, and you won't find that at SA or Dicks (if you're serious about getting a comfortable pack).

Good luck!

spcfa and ShelliDawn, I had no idea about an outfitter. What a great idea. Thanks for the tip. I will do some local reasearch to find someone who can meet this need.

When it was time to replace my old Rick Steves backpack, I went to ricksteves.com and bought 2 similar to my old one (3 sections) The largest compartment just holds my netbook flat against my back with a few clothes. The shoulder straps are well padded and there is a sturdy hanging strap on top.
If you have access to an REI store, you can find a quality backpack that will meet your needs.

KeppieAngel, if I'm correct in thinking that you're going to check the roller but you want a carry-on bag that is large enough to carry more clothes but still legal, then it sounds like what you want is a carry-on backpack. Here are a few good options:

http://www.gaiageek.com/travel/gear/the-best-carry-on-backpacks

Something to consider though: if you're doing this on a budget and you won't be having a taxi take you to the door of your hotel, you may want to consider ditching the roller altogether. Europe is full of cobble-stoned streets (not smooth and not fun for wheels) and places with no elevators (subways stations, small hotels - don't be surprised if you have to climb 4 flights of stairs to get to your room). With a large enough carry-on backpack you may be able to get by with only that and a small handbag as your personal item, checking no bags at all. Or, you could get a full-size backpack to use as your checked bag and then a small daypack for the flight. When moving from A to B with the bags, you simply wear the small pack on your front. Alternatively there are some full-size travel backpacks that have detachable daypacks which can hitch on to the back of the main pack.

Which ever setup you go with, I think by the end of your trip to France you'll have a greater understanding of the wisdom of the backpack. Have fun and enjoy the French food!

kentchristopher - gaiageek is a good link. Just enough info not to overwhelm. I think I will still take the roller carryon because I know it meets carryon limits. I am using reward points for my hotel stays so I can rationalize the cost of some taxis and all the hotels I will be staying at major chains designed for business travlers with elevators and a bell staff. I wanted to take a backpack not because I am taking a laptop but because I may be taking a train and thought it would be easier to have a backback and one piece of luggage. Also, if i decide to fly instead of taking a train on Air France - they accept one carry on and one checked bag. The good thing is that I am also using FF points to fly to Europe and I am going business class so I am allowed to check two bags - no charge. It was just a concern that my within France planes and/or trains had baggage restrictions or that it would be difficult to maneuver two pieces of standard luggage on a train by myself.

Merci,
KeppieAngel

DH and I each use a Rick Steves roll-aboard and a Rick Steves Civita Day Pack. We have more than enough room for a 3-week trip. We did learn to pack a folding expandable duffle inside one of the roll-aboards to accommodate dirty clothes or souvenirs on the way home. Really didn't need it if we were careful. Less is definitely more when traveling.

DH and I just got these earlier this year and we love them. Lightweight, have a laptop sleeve, comfy straps, hold a lot (one big compartment that loads from the top which is hard to get used to but now I love it), have a front compartment with lots of pockets and zippers for keys, passport, etc., and my favorite feature is a wide strap that allows it to slide over the handle of your wheeled luggage and stay secure.
http://www.eaglecreek.com/bags_luggage/everyday_backpacks/Quirk-60186/
We also have Eagle Creek wheeled bags which we have had for years and their customer service is amazing, with a lifetime warranty. After more than 10 years of regular use DH sent his wheeled bag back to repair a cracked wheel and they returned it good as new for free and even cleaned up the bag -- all he had to pay was the shipping.