Huge brain dump here of what I do say to day with DD(5) and DS(7) and have done for several years.
correct her / others as soon as the stereotypes come out. If someone comments on her looks, make sure you balance it with a comment and her achievement / talents.
Outright 'No, girls can be pilots - let's look some up' or 'there's no such thing as girls and boys toys'.
Actively DONT comment on other girls' dresses / hair etc but instead ask a question about what they are doing / feeling.
Find role models in your family / friends that buck 'traditional' roles - we have a female cousin police officer, a mum friend who's a GP, a male friend who's a teacher, a female scientist, my brother does all the cooking in their family etc etc. And talk about them a lot.
Point out the same on TV / films.
Praise girls for doing 'boy' things eg strong, brave, running and praise boys for 'girl' stuff eg creative, colouring nicely, being kind, looking after dolls / toys.
I've yet to actually deal with the societal issues of the patriarchy but I think I do occasionally and casually point out that the world is set up for men which makes it harder for women (I can't reach the oven clock etc!).
I think I may attempt to explain marketing soon as DS(7) could probably get his head around basic idea and how it's aimed at people but doesn't mean that ONLY those people like it.
I also try to centre women in DDs world by all neutral things eg animals / odd characters are female eg 'oh look DD there's a squirrel digging - I wonder what she's looking for'
I intend to talk to them both about it as much and as soon as I can so it's not a big conversation at a certain point but more an ever present lesson on how to smash the patriarchy 