Yes, you can buy stuff on Amazon using
BTC. There is a wallet called Ipayyou (it is 2 years old age now) that allows you to buy on Amazon using your bitcoins. The wallet has a featured called Amazon Direct that lets you transfer any dollar amount of bitcoin to use for purchases on Amazon. I might be mistaken but I think this is the only way, for now, to buy things on amazon using bitcoins.
For more information check:https://bitcoinexchangeguide.com/ipayyou/
or visit :
https://wallet.ipayyou.io/Never heard of ipayyou. So people should be careful when using such services with less reputation. Anyways, you can also buy amazon giftcards from reputed shops online that sell those cards for bitcoin. Much safer option I guess. Or you can use purse.io like others mention, but as far as i know, there are some countries they do not support.