There's a sweet spot in packing these days that will save you a lot of grief and hassle for international travel. If you can fit all your stuff into a carry-on and can still lug that bag around easily despite stairs and cobblestones, you're set for almost any situation and any airline. This 52-liter travel backpack from Eagle Creek hits that sweet spot quite well.
It's a travel backpack, which means you can use it as a backpack or zip the straps into a compartment and make it a suitcase - as in when you want to check it for a flight or upon arriving at a swanky hotel. Unless you totally overcram it to the gills, it meets the requirements for an overhead compartment bag. Since it doesn't have wheels and is made from lightweight materials, it's weighs less than 2.5 kilos (5 pounds, 4 ounces).
This doesn't mean it won't hold a lot though. There is a capacity 3,150 cubic inches (52L), with lots of zippered compartments and two side pockets outside. I like this model though because it dispenses with the zip-on daypack, which to me always sounds better in theory than it works out on the road. There's a cinch sack inside the bottom compartment which allows you to keep dirty shoes or laundry away from the rest of what's in there. An external front pocket and a zippered smaller pocket provide places for smaller, quick-access items.
In my test during a recent trip, this pack performed admirably at it will probably be my main go-to bag from now on. I was able to use the side strap or top strap when it wasn't on my back without it dragging on the floor and the straps were comfortable when I was ready to go into backpack mode. I was using it in New York City and had fun breezing past all the wheelie suitcase people struggling with subway stairs, escalators, and the never-ending construction at JFK.
The drawbacks? The zippers felt kind of grabby and not all that rugged to me. But with a lifetime guarantee, maybe there's no worry and they just need breaking in. If you're traveling around the world in varying climates, this bag might not offer enough capacity and you may have to resign yourself to 70 liters and always checking it for flights. If you're just going to one spot on the globe for a short time, however, this model should be fine if you pack right. At a list price of $180, this is priced below many comparable packs.
Note that this is, for some odd reason, listed as a 55-liter pack when you're searching product listings online. Rounding up I guess...
Get the Eagle Creek Meridian Travel Pack at Backcountry.com
See more on this bag at EagleCreek.com