From a guy's perspective, 10kg is more than enough for a week or even two if you're traveling as a tourist and don't mind doing laundry. I'll wash socks/unders in the sink at night and hang to dry. Fast-dry stuff is just amazing! Or if my B&B/hotel offers laundry facilities I'll use that time to research my next outing and to get a little break.
I'm going for 6 days and will have packed 2 button-down shirts, 2 T-shirts, 1 pants, 3 socks/underwear, plus what I'm wearing onboard (which will include a fleece hoodie and rain jacket, plus my 3-1-1 toiletries kit (with minimal stuff--again, only 6 days). No extra shoes. I have a lightweight laptop and carry my phone on me. Only optional extras I'm bringing are my pipe and tobacco, and a windshield mount for my phone for use as a nav-aid. In a carryon duffle all that weighs in at 6.7 kg. I'll even have room and weight to bring back a nice Aran woolen sweater and a few other small things. If I have to, I can offload a few things in my vest or cargo pants on the way back.
My logic here is that as a tourist I will never see the same people twice (or more accurately, nobody will see me more than once), so if I reuse a shirt/pants combo who cares. I usually wear my shirts twice before laundering (slacks 3x) anyways so why go overboard on vacation. I wear cargo pants for extra carrying capability if needed, and a Scott-E-Vest hoodie that all my electronics fit in (including my laptop), and the vest with all that stuff goes through the airport X-rays. A vacuum space-saver bag keeps volume down in the bag allowing it to fit a bit more for the return. Now if you're going for business meetings or for a month with family, or are bringing a ton of hiking gear then yeah, check a bag and have some peace of mind.