From the CISOs I talk to, the only definite point is that they all come from very different backgrounds, but have a wide range of experiences...not just in the security industry (sometimes not even in the security industry)
Aim for a wide range of business experience, as at this level talking about security doesn't tend to have as much impact or value to a company as being able to talk about business risk, governance frameworks and value.
I wouldn't class any single discipline as 'more valuable' unless you count strategy, governance and business risk as disciplines. You'll want to be able to understand at a broad level what your teams across all disciplines are doing to help your organisation reach its preferred risk level at an acceptable cost.
This article from ComputerWorld UK titled "How to become a CISO" might also be of interest.
Also have a read through all the questions tagged professional-education - as there is a lot of useful information in there already.