From other OCers previous experience (in both Auckland and Sydney), the CO doesn't tend to ask for proof of savings etc.
BUT, it never hurts to be prepared. We took a document which we called 'Personal Financial Statement - Mr Emily and Mrs Emily'. There we listed all our assets and liabilities in AUD and, at the end, showed the conversion to USD. Backing that up, we had a copy of the most recent statements / proof for each asset (e.g. superannuation statement, bank statement, house appraisal, mortgage statement). I also took a letter from my employer showing my salary at the time, to prove I was working and that I could support our family.
It was absolute overkill but, if nothing else, I wanted to make sure the CO knew we had prepared and considered everything. We didn't need it in the end, and I was kinda disappointed because I put alot of time into preparing it!