I guess this is less French and if I have to pinpoint it, South American, but on long haul flights I take an outfit change with me, loungewear-esque on the plane (a sweater dress you can cocoon up in and warm natural fibre tights are actually a good one), good comfy thick socks, YY to a giant scarf and I put my coat in with the luggage at check-in. Also have a small toiletry bag, like a sheet mask for during the flight as I shrivel up at an alarming rate, deodorant (not a spray) and toothbrush + toothpaste just before landing (though remember to keep a water bottle around until then as you can't drink the tap water in the toilet) and change back into normal clothing so I feel less like a boiled in a bag ready meal upon arrival.
For in the US, it really depends, if it's a convention hall and it isn't busy it can be quite chilly, if it's busy, it can be boiling and people happily walk around in short sleeves. I find that most US indoor climates allow for year-round wearing the same clothes regardless of season. If it's a 'smaller' conference in a business hotel I'd expect temps to be comfortable everywhere except maybe in some odd hallways.
Elle, I was wondering about the length too, but I think it's thrown off by the shoes. They're really quite high and we're not really 'used' to seeing that anymore. Normally with the introduction of silhouette changes, heel heights change with it and we haven't really seen that. It probably has more to do with female emancipation becoming such a hot button issue over the last 1.5yrs. Even the diminutive kitten heel isn't really catching on, we only really see heels in boots and they're not neck breaking height and tend to be sturdy.
Rosie, I think in between Kiko and Tom Ford, Estee Lauder Pure Color Envy is a good pick for moisturising and long-lasting. Though, if you're a subconscious lip worrier or licker, very few lipsticks will hold up to that. I think 'Boldface' is their cool red.
Catherine, it's semi-sheer but I tend to prefer that with darker reds as they can be a bit full on, but you can try Lipstick Queen 'Medieval'.
Very impressive feet on the macaron shells there, good shine on them too, Elle. I'd wear a less fancy version of attached, washed silk (or otherwise floaty blouse) worn open a touch low (camisole optional), low rise slim fit jeans, a good belt with a bit of decoration, western style boots, battered old leather jacket or bomber and a scarf with a bit of an ethnic feel. Mishmash jewellery, either stacking a few delicate necklaces or bracelets. Smudgy kohl around the eyes and forget about lipstick as I can't be arsed with reapplying all night. Although I don't think anyone but Brits (the Irish, maybe?) actually do hen nights, so my take is probably useless in that regard.