Buy a thermos and carry hot water. It will stay piping hot for over 12 hours.
A little different but you can also buy ready to feed formula in little bottles which are a massive help!
Rapid cooler! I just take that with a flask of hot water and the formula
Against guidance (but without any issues at all) we pre made and stored in fridge from baby being a few months old and ever since, he has preferred them cold and never has to wait for a bottle being made. Before that, Nuby rapid cool x