Amazon has a promotion on their own devices for Discover cardholders. You can get a discount of 25% when you use cashback from your Discover cards for at least a portion of the purchase. You can use just one points or one cent in Discover cashback in order to get the discount. The promotion is targeted so it will not work for everyone.
On top of that discount, some of these Amazon devices already have discounted prices for Prime Day. Worth a look if you have your eyes on any of these gadgets.