Niantic Labs via Pokemon Go is offering select Pokemon Go: In-Game/App Items for Free when you apply the listed promo code 5PTHMZ3AZM5QC (must be logged into your account).
10x Pokemon Ultra Balls
An ultra-performance ball w/ a higher catch rate than a Great Ball
10x Pokemon Max Potions
A spray-type medicine that completely restores all HP of a single Pokemon
1x Pokemon Sinnoh Stone
A special stone originally found in the Sinnoh region that can make certain species of Pokemon evolve.