ALWAYS check with the airline you will be traveling with for their weight restrictions and allowable dimensions for your carryon (and your checked bag if you have one). These vary from airline to airline, but especially from North America to Europe - European airlines are notorious for having extremely low weight limits and ridiculously overcharging you on every kilo you may be over.
See my carry on backpack comparison here.
Some airlines now charge for a “large” carryon bag too so if you can get away with staying in their “small” category you can avoid paying unnecessary baggage fees. If you can pack two weeks worth into some of these airlines free 'small' carryon bags please let me know your secret! ;)
Here is a listing courtesy of worldtraveler.com of the maximum dimensions and weight limits allowed on some of the major airlines: http://www.worldtraveler.com/international-carry-on-size
And another for some of the major European airlines courtesy of skyscanner.net: https://www.skyscanner.net/news/cabin-luggage-guide-hand-baggage-sizes-and-weight-restrictions
This list is fairly comprehensive but dates back to 2009 so not sure how accurate the information is: http://flyingwithfish.boardingarea.com/2009/06/28/carry-on-weight-baggage-limit-chart-for-65-world-airlines/
Always double check your airlines restrictions (and if you will be traveling with their partner airlines) before traveling, because weight and size limits may change from time to time.