A little differing opinion here, as I always take the soft sided collapsible cooler with me. I have two of the big daddies (72 can capacity, I believe?) and a smaller 48 can capacity. I usually take one large and the smaller with me for 6 of us.
The large I use for milk, juice, and sodas (we drink a lot of those) and water and use the smaller for lunchmeats and other sandwich stuff (lettuce, tomato--that kind of stuff).
To keep from using room in luggage, I've done a couple of things. I use them as luggage, if needed and check them on through. I have also used them to carry my trading pins, bath supplies (we always take our own shampoo, bath and shower get, etc) or I've out snacks for them room in them.
I am never without my soft-side coolers.
BTW--they fit great under the sink at the Dolphi. Easy to access, yet, out of the way.
I think we got all of ours at Wal-Mart, but, I'm not sure. Maybe one from Target????