June '03 we brought a soft side as a carry on. As long as it fits through x-ray it's okay. The Security people even questioned me what was inside due to the plastic water bottles showing a funny picture on the x-ray. I honestly confessed what was inside, Water, Beer, Juices, Sodas, etc. No problem they said and we went on through.
The Cabin Stewards even leave a card out for when you would like ice service. I think it was morning, noon or night. I checked off morning and night and got what I wished for.