I can think of a couple solutions for portable hot water though they are not traditional kettles. I found one of these Zelco Brisk Brew single cup coffeemakers still in the original box with an unwrapped cup. It has a switch on the back for selecting 110 or 220v for use overseas too. This is as compact as I have seen though I have an old Hot Shot that is pretty compact as well with more of a box shape than the newer style but works the same way.
The Zelco and the Hot Shot can replace a bulky kettle but will not hold as much water either. I like the Zelco since it can brew coffee too (built in mesh filter) if the pour over cone gets lost or broken but the Hot Shot will be easier to find.
A microwave will heat water too which requires no additional equipment besides what is already provided in a standard hotel room, and depending on the maker, some hotel drip or single serve coffee makers deliver decent temps too.
Sunbeam Hot Shot - $18

Zelco - $??
