When we took our first cruise with our 10 month old I used bottled water, powdered formula and platex disp bottles. This way I only had to wash the nipples and rings. I heated them by filling the sink in the bathroom with hot water and then putting the bottle in it. It only took a few minutes because I would fill the sink so the water covered all of the bottle but the nipple and because the liners is much thinner than a plastic bottle it warmed really fast.
I could never give my kids cold milk either.