I read somewhere Jerry's favorite beer was Anchor Liberty Ale.
But an online search to confirm my source discovered these other possiblities...
Sierra Nevada Porter
"Gradually sales began to grow in Chico, where the large population of students at California State University had a healthy thirst for beer. Distribution was later extended to San Francisco, where the beer was discovered by Grateful Dead guitarist Jerry Garcia. When word got out that Garcia loved the firm's porter, many of the band's loyal fans began to seek out Sierra Nevada's beers."
Sammy Smiths Taddy Porter
"...was one of guitarist Jerry Garcia's favorite brews.", " "A fatty porter" popular with Jerry Garcia when the "Dead" toured London; a classic; flavors border on stout with just enough sweetness to make this a tasty porter!"