Flying with a baby

Ok so... travelling from the uk to the USA in June when baby girl will be 3 months old. How do you do formula on an airplane?? At the moment we are combination feeding because my boobies don’t want to make enough to feed my 9.5lb goober but I’m hoping this will change by end of June... if not though we will have to formula feed on the plane as well as boobies sooooooo - how do you do it?? Eugh!! So many questions - why can’t babies come with an instruction manual!?! Help!