The World Series between the San Francisco Giants and the Detroit Tigers is technically a medical marijuana series. Both cities honor respective state laws, which carve out criminal immunities for medical marijuana patients. But, legally, California patients visiting Michigan have an easier time of things than Michiganers (-ites?) visiting Cali. Michigan honors medical marijuana recommendations made in California. California does not offer such reciprocity.
“There are 17 states that allow patients with doctors’ recommendations to use medical marijuana, but only five—Arizona, Maine, Michigan, Montana, and Rhode Island—include reciprocity,” noted the Marijuana Policy Project, yesterday, in a release.
“So," the release asks, "how does a medical marijuana patient travel?"

TSA agents turn over contraband and passengers to local law enforcement, so it's the local city's policy that applies. For example, Oakland and San Francisco airport police have stated in the past that they respect state medical pot laws. You can call the airport police ahead and ask for their policy on medical marijuana, just to be sure.
“So there you have it,” writes MPP's Dan Riffle. “No word on whether two-time Cy Young winner, World Series champion, and noted marijuana user Tim Lincecum is aware of the policy.”