Jeans or baggy Indian trousers, a long Indian-style top (at least I will look original, if not smart!), a long scarf (cotton or wool depending on the season) and a long cardigan. Even if it's a plane trip from 32 degrees in Accra to 32 degrees in Rome (my most frequent route), planes are freezing! A pocket is essential, not for phones and keys, but for passport and boarding pass, so I don't have to fish through all the junk in my handbag. Birkenstocks in summer, Campers in winter.
If I am checking in a case, I take just a small bag on board for phone, iPad, keys, book and valuables. It has to have enough spece to stuff in the cardigan when I arrive.