Titanium.

The MSR "Titan" titanium kettle is a neat little unit. Just right for popping on the biolite stove to boil up some H2O for a coffee or tea. Titanium is incredibly light (although I don't require the weightlessness), incredibly expensive (noone requires that), incredibly strong but there is no fear of ingesting any of it with your food since titanium is generally used in the body anyway for fixing people up.