Yes, a backpack on the Lido deck while waiting for the cabins to be "ready" is a geat idea, thanks!
Besides my small rolling carry-on bag with a handle for my clothes, I have a small backpack that I'm going to use to hold my netbook, purse, travel docs, meds, electronic stuff, etc. on air travel days. So I will just dump my carry-on with clothes in the cabin closet and make sure to close the cabin door. Then, I will have my backpack with everything I need or of value on my back, while I go back up to Lido deck for lunch. Then I also don't have to be in such a hurry to get back to the cabin at 1:30.
This way, all my valuables are still with me, on my back, and if someone wants my clothing that badly, well I can always buy more in Key West.