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I pack light. I make everyone who goes with me pack light (except don't ask my husband about Japan, that was a fluke). You should pack light and take only carry-on. We have been to Europe for six weeks at a time with a roll-on suitcase and a daypack each for my daughter and me. Who are you trying to impress, anyway? Neat, clean and well groomed are largely what you need, and you can achieve that exceedingly well in carry-on. The museum guy really, really doesn't care if you wear the same shirt twice. You don't need the ball gown, and the little black dress rolls. Leave room in those carry-ons for your take-home goodies. Take a great blazer and wear it onto the plane if you need something really spiffy.
My suggestions, honed over dozens of trips, are below. I concentrate only on women, since my husband would take two shirts, two pairs of underwear and socks and one pair of jeans and tennies for the whole trip and call it good. That's nice, because I can use his suitcase for my stuff, especially the take-home goodies! He's one of those disgustingly clean people who always looks tidy. Wish I had his luck. My daughter and I, well, we do other things, as below:
OK, you have enough clothes now for about 1/2 the max size carry-on suitcase. Trust me, I know! The way you pack is to roll. Lay down one pair of the pants and lay 1/2 the clothes over it. Repeat for other pair of pants. Now, roll tightly starting at the cuffs, like you would a sleeping bag. Your clothes will get there in better condition and in less room than with any other method. Don't bother buying the bags that suck air out, this is free.
Plan to wear your bulkiest items on the plane including the tennis shoes, and pack the other shoes. Insert toiletries, and you have a loosely packed suitcase that stays organized even through airport inspections but will allow you to slip goodies in all around the edges as you go, plus those shirts that were a steal in Florence.
So what do you do with the daypack? Easy, your in-flight entertainment, your medicines and your camera. Those are the things you really don't want to lose, if for some reason they make you check the carry-on. They won't ever make you check the backpack, unless a real emergency happens - and then you won't care! You'll have travel insurance after all, won't you, they sell everything you have there, and you can access your itunes and audible from Europe to reload.
My case holds an ipod with 20-30 audio books and music, 1 recharger and batteries for the recharger since the Ipod won't last me for more than 8 hours, my Palm Pilot with at least 40 books on it (on a chip, also has music in a pinch - I also have a backup chip in my camera case) and its recharger, two pair of really good earphones, the FM car player to bring my music into the destination car if appropriate (have you ever heard Dutch rock and roll?) and at least 3 paperback books plus an LED book light/flashlight in case the electricity fails completely somehow. Guessed yet that I'm a reader, deperately afraid of running out of books?
I also pack my camera in its case, my purse w/wallet that I will use in towns, my travel docs, and my meds and a toothbrush/paste. The pack empties when I am in a hotel, so it's useful on shopping trips to go get the bread, pate, wine and cornichons for lunch in the Perigord.
My last suggestion: if you can't pass up that bargain and it won't fit in your carry-on, everybody ships!