They last better, too, so you can reuse them for more than one trip. Just put the smaller ones inside a larger one and leave them in the suitcase between trips.
I find that the sort with the little zipper gadget on them are quicker to deal with, though they cost a little bit more. I use 2-gallons for the grownup clothes, and gallon-size for the kid.
I also use a larger clear bag (the sort blankets come in) to hold beach towels, then I pack them in the carseat satchel. That pads the carseat and makes things easier if the satchel needs to be searched. (We always go to the beach, too, so we take our own towels.)