I almost always take a hot water heater on my trips. I have used this one for years. It is dual-voltage and trustworthy, but unfortunately takes up a lot of space in my bag.
An immersion-style heater [below] would be more compact, but all the reviews for them on Amazon that I've been able to find seem to indicate that most fail after a few uses. Does anyone know of one with either a replaceable fuse or that they have used reliably?
I know this would not be an issue for normal people, but I need at least one cup of coffee before I leave my hotel room! So a hot water heater is an essential item for me.