I take a sarong type gauze fabric wrap that works and actually looks nice, or my ultra thin silk kimono which is a robe but which looks (sort of) like a geisha costume. Neither takes up any space in carryon.

I also love the travel shower shoe/slippers I get at Magellan's http://www.magellans.com/store/Cloth...n___ShoesTS491
which are about as large as an envelope, last a LONG time, and can be worn in the shower or pool if you're skittish about whatever. All it does is bleach them whiter.

I used to wear them through security until some TSA jerk was afraid I could hide a bomb in the paper thin (probably made of paper) soles. An agent in the same airport had congratulated me on my ingenuity on my international arrival flight. Now I wear OR shoe covers.

I guess the ultimate pool wear would be disposable patient gowns...maybe officious hotel staff would prefer robes?