I've needed a 9 mm wrench several time on bike components and the 16 mm is useful for other things but a 5/8" SAE will substitute for it in a pinch. Of course a socket and combination wrench set in both metric and SAE sizes doesn't have to be limited to bicycle work. Cars, appliances, etc. all need work occasionally.

+1 to FBinNY's advice. Premade kits are going to contain tools you never use and it's more efficient to buy specific tools for specific jobs. There are a couple of general purpose tools any bike owner who has any interest in mechanics should have and that's as set of metric allen wrenches, a set of cone wrenches and a good chain tool. Beyond that buy for specific components.