What we usually do is buy a case of water and put the whole thing in a duffle bag. I've had security call me down once and when I showed them it was an untouched case of water, they said OK, you're good to go. I then use the duffle bag for dirty laundry!
Mariner-05/06 & 10/09
Oasis Inaugural Cruise-12/09
Monarch-03/10 & 07/10
Mariner; RSS- 10/12
Australia; Celebrity Solstice 11/27/2016