I'm taking the bottom half of his two way booster, so he's the right height for "seat belt doing horrible things to his internal organs" prevention. I am not taking the back as here they have tether straps, which won't work on a bus as they won't have the bolts for them. Without the tether it would do more harm than good in an accident. Also it weighs a ton all together and I am going on my own, and ds and a suitcase and our picnic (because airlines don't do gluten free, egg free food on Trans tasman flights) and our handluggage...
I was taking a bus rather than a taxi because of the car seat, and here I am taking a car seat!