I have a steadfast rule when traveling – carry-on only! Even for international trips that are two weeks. I would argue – especially for those trips. Note, this was when I was traveling without kids…
Why? One – I always have my bags with me so they can’t get lost. My parents once convinced me otherwise when we went to Paris, and our luggage was lost pretty much the entire time we were there. The worst thing was that all I packed would’ve fit in a carry on, but my mom wanted me to bring a bigger luggage to store gifts. If you’re not willing to do carry on only, I recommend having at least essentials in a carry on bag (medications, contacts, toothbrush, one or two changes of clothes..).
Two – if traveling to multiple cities internationally, you’re most likely taking a train. Which means your luggage is likely not able to be stored close to where you sit, which means greater chances of it being stolen. If you have carry on baggage, you can keep it with you.
Three – the places I’ve visited in Europe don’t always have elevators or perfectly paved streets. Carry on baggage (choose ones with straps or are like back packs) are a lot easier to handle in those circumstances than ruling luggage?
But how do you fit enough for weeks of travel? Easy – launder your clothes there! I usually choose places with a washing machine available (Air B&B’s) or just prepare after of time by looking for a place that will do laundry for you. Have enough for about three changes of clothes and just alternate outfits. I did it easily in intranational travel, and I’ve definitely did it in two different two week plus international vacations in Spain and Italy. No regrets!