We need to bring two of the backless booster seats with us for the rental car. Also will be bringing heavy jackets (just in case, trips in late Dec.). My question is can I just buy a big old duffel bag to put the bulky and odd shaped things in? I'm assuming there are luggage size limits for airlines. Would I just see what the luggage size limits are for Delta and then find a duffel that meets the requirements. This is my first time flying in 6 years and our first time flying with our kids. I'm open to any suggestions for getting the stuff from austin to orlando. Thanks.