I don't think that you would be able to buy anything directly using bitcoin on ebay or amazon as they have not yet started to accept bitcoins as a mode of payment so then only option left for you is to sell them and exchange for fiat and buy the using COD method.
This is the best way to do ,as he mentioned ebay and amazon doesnt accept directly bitcoin as payment . Since it isnt available as of now then the last best way is to convert directly you bitcoin to fiat by your local wallet provider you could able to exchange it.