It's actually a booster for my 4 year old - he can't use it on the plane so we'll get that part out of the way, lol. I am going to gate check (that seems the safest as it will make sure I definitely have it when I get there - sadly, not Disney). I do have a carseat bag, but it doesn't offer much padding so I was going to either, 1, try to put the booster back in the box it came in and put that in the bag or 2, pad it well with other stuff. So my question is, how much other stuff can I use as padding? I'm flying US Airways and its the first time I have to deal with baggage fees (I'm usually a SW girl but they don't fly to Charlotte). I was going to at least put my son's swim stuff (puddlejumper vest) in the carseat bag. Our stuff fits in one suitcase. I don't want it to seem like I'm trying to get away with something by packing stuff in with the booster, but I want it to have plenty of padding, too! How strict are they? Anybody disagree that gate checking is best?