Helmet, shoes, pedals (yes power pedals are neccesary), garmin etc. all in carry on. Take at least one full kit in carry on as well. Helmet can clip to outside of a rucksack, i also have neatcleats to clip shoes to outside of a bag.
when i pack my kit i put a base layer and a pair of socks into a jersey pocket, i then place the jersey onto a pair of bibs and then starting at the legs fold an roll the kit into a sort of sausage shape and then use the bib straps to kind of tie it all togeather. Then you know that one roll (or sausage) is a full kit.
remember if you’re out cycling all day then you won’t go through nearly as many ‘normal’ clothes