Update: I received 4 Starbucks gift cards on the last promotion. I just received ANOTHER Amazon gift card as well.
This one is a bit tricky and requires a little effort and referrals, but it will earn us both a gift card.
Sign up for a Nextdoor account. It is kind of like a Facebook site for your neighborhood. After you do so you have to sign up 10 of your neighbors.
They make it easy to sign up neighbors, they will send a postcard out to them for free.
Here is a picture of two of the 4 I received last promotion.