Very, very, very big numbers.

If you want to read where all those dollars (31 billion of them) were wasted in Iraq and Afghanistan, here is the link to the Commission on Wartime Contracting's final report to Congress. The report found that the US military has over-relied on contractors - 260,000 of them in total, sometimes outnumbering the number of regular military forces - and was "unable to provide effective management and oversight" over the $206 billion it took to pay them. Think of very big numbers, then double them lots of times and that gives you an idea of how much has gone down the Swannee.
The report also notes that between October 2001 and July 2011, 2,429 contractors were reported by their employers to have been killed in Iraq and Afghanistan. There were 6,131 U.S. military fatalities during the same period.