Google Cardboard is a head-mounted-display adapter for touchscreen phones.
Kellogg's Captain America: Civil War Promotional
Kellogg's had released a promotional item (free with 3 Kellogg's, Keebler, or Cheez-its products) which is a basic Google Cardboard device.
It lacks a button input, but not bad for 'free with proof of purchase'.
I have created a QR code for easy use of the viewer with the Google Cardboard APIs: