Well, I've done four weeks in Paris and London with small nylon backpack designed to hold a small laptop computer that weighed under 12 pounds so it certainly can be done.
On the plane, I wore a pair of lightweight, straight-legged, black pants; a lightweight cream sweater, a tan trench and my walking shoes--a black, Oxford-style shoe that I rain proofed. In my pack, I had a pair of light-weight black sandals, a couple of washable silk tops, a black silk cami, a pair of widelegged black silk pants, a black cashmere cardigan, a change of undies and socks, a couple of scarves, a pair of yoga crops for lounging/sleeping, and a man's underwear t-shirt I wore for sleeping. Everything fit easily in a medium packing cube. I used one of the small mini-bags that are included in the SportSac bags for my toiletries.
If you think it was a lot of black, you are right. My only color was in my silk tops, my scarves, my cream sweater, and my tan trench. Black just works in cities, day and night. My evening outfit for dinner and the theatre was my black silk pants, cami, sandals, and cardigan worn with earrings and a cuff. My hot-weather outfit was rolled-up straight-legged pants, a silk top, and sandals. My beach outfit was my cami, yoga crops, and cream sweater. On a cold, rainy day in London, I wore my black straight-legs, the cami, a silk top, my cream sweater, trench, scarf, oxfords, and trench. My wardrobe pretty much covered every situation and event, but I did spring for some cheap beach sandals that got tossed before we headed home.
I actually was never asked to put my bag on the scale at RyanAir or EasyJet, although most people had to do that when picking up their boarding passes. The only thing I can come up with to explain this,is that the staff thought my bag was just a handbag, not a carryon.
Oh, and I'll just add that I purposely didn't layer on the plane because 1. I knew I'd have to find somewhere to stash the extra clothes while traveling between destinations, and 2. I dislike feeling bulky, hot, and uncomfortable on the planes. The discount airlines tend to cram as many people as possible on a flight and those seats and overhead bins can be SMALL.
