Shoes for long flight

I find slip-on shoes more comfortable on inter-continental flights as it allows me to take them off if I feel like it, and it's easy to wear them again without feet feeling sore. While I haven't used them, some people advocate wearing flight socks that prevent your feet and ankles from getting sore.

Most times when I fly with budget airlines though I don't have space to pack two pairs of shoes as I take only carry-on luggage. In this case, I wear my running shoes, but ask for an aisle seat during check-in which gives so much more space to stretch my legs. The same helps during long-haul flights too. I also check up SeatGuru for crowd-sourced data on what seats are best on a particular type of aircraft / airline and then ask for those ones during check-in.

I'm a fan of just taking off my shoes if I'm not wearing sandals.

For a long flight I would always go with flip-flops. When flying long distance carriers always provide a commodity bags where you can find some sockets. So basically if you are scared of getting cold (because it is cold up there) you can just put them on.

In order to be polite, I go until boarding with regular shoes and once in the place switch them.

I don't have room in my carryon for a set of shoes that are just for the airplane, so whatever I wear on the plane needs to also be what I wear in the airport. There's a lot of walking so it's vital the shoes be comfortable - I choose them carefully. Flat pumps work for me and they slip off on the plane if I want to tuck my feet up under me in my seat or just give them a bit of a rub. Tieing and untieing shoelaces in the cramped confines of an airplane seat is a non-starter for me. You can find pumps and get your feet into them even if you can't see them.

Whether or not the airline provides socks for you varies wildly. SAA is the only one I've got socks from in economy. Generally everyone gives them in business.