Honestly, bills.  Electric, gas, water, Internet, house payment...  

Reason is two fold.

• It would save me the hassle of transferring coin to an exchange to wait for the fiat to come back to me to pay the bills.  (faster/less headache)
• CONFIRMATION - I absolutely hate it when the other party makes "billing mistake" that is never in my favor.  Being able to prove my standing instantly with blockchain would be amazingly helpful