The answer will depend on what year it has happened and what is the value of bitcoin at that time. Let us not go back to the past and say that pizza was the mos expensive things bought, the reason is that bitcoins value at that time was so small so we can never say that that was the most expensive things that was sold in exchange for bitcoin. The most expensive thing or item that was bought using bitcoins in history considering the value of bitcoin at that time was a car and a piece of land. Even if bitcoins value was low or not but the fact that it was sold at hundreds of thousand of dollars worth of bitcoin.