With many economy level flights to China from the US.....Layers, and elastic waist bands! Layers because I've been cold AND hot on planes. Knit pants (I don't usually wear leggings, but have some slim fit knit pants), knit tee, sweater (usually a long merino cardigan for cooler weather travel) scarf, comfy bra (no underwires for long flights - I've never had a problem with security screening but I have a large bust and don't want ALL THAT wire cutting in to me at hour 8 ;-) I still wear my heaviest shoes on the plane so I don't have to pack them, but bring a slipper (and a shoe bag for after the flight!) to wear - has to have a rubbery sole for the lavs!) I always wear black - I wear it a lot anyway, but also because I've had people spill red wine on me. Hopefully in business class you'll have a better experience!