I have found that each time I travel to Europe I take less with me. On my recent trip to Austria (July,2014) I took only my backpack/rolling bag and found it quite liberating. I use a Patagonia MLC Wheelie, measures 21x14x9 and I could easily live for a month out of this bag because I have found a few accessories that make packing easier:
1) Sea to Summit Co. makes a daypack called "the Ultra-sil daypack", this is so compact that it packs to a size smaller than your fist. I put the daypack in my main bag on the airline and then use it daily for rain jacket, camera, water bottle,etc.
2) I use the Rick Steves large packing cube for shirts and pants and two eagle creek packing tubes for underwear and socks, a Rick Steves toiletry bag (small one) for meds, shaving, toothbrush etc.
3) I have a Marmot Mica rain jacket that folds up to a very small package and I bring a Kuhl fleece pullover that is thin and packs well. Using a Lightweight waterproof shell and lightweight fleece pullover together allows me to stay warm down to around 40 degrees F.
4) I search the internet sites for sales on many of these items and can usually by them at greater than 50% off, I have found that the clothes that are made from nylon or polyester material not only wash and dry easily while traveling but also lay flatter and pack easier. All the shirts I take are long sleeve but have the button up fasteners so I can wear them in the heat of summer.
5) In cold weather I take a Patagonia Ultralight down jacket that packs into it's own pocket and basically the same clothes except I take very thin long underwear (hot chilly's) and wear them under my pants and shirts. I will usually buy gloves and a knit hat after I get where I'm going.
I have found that by getting everything into one bag only, that passes all the airlines rules, it has made travel so much easier, I will admit that I don't carry a laptop, I only carry a Apple mini iPad.