Sp17:
Each semester 16A has a meme contest where some small amount of extra credit is awarded to the most popular memes, within the constraints of the contest rules (i.e. has to be course content-related, has to play nice, etc.). This is one of my favorites of all time, even though it wasn't eligible since it technically wasn't about course content.
Fa18:
In an effort to bribe my way into student engagement, I brought snacks whenever students caught me making a mistake in discussion. Although evidence at this point is purely anecdotal, it seems fruit snacks are a viable alternative to cookies (Hessler et al. 2018. 10.1111/medu.13627), especially for those with dietary restrictions.