Yebisu is Misato Katsuragi's favorite brand of beer. Her refrigerator is filled with dozens of cans of it. Misato has been known to routinely start her day by waking up and then chugging an entire can of Yebisu beer.
"Yebisu" is actually a real-life brand of beer in Japan. When the series was originally broadcast in Japan, the TV network the series was airing on complained that they didn't want to advertise for Yebisu for free like this, so by Episode 02 the name was changed to the fictional "Yebichu" (named as a direct homage to the manga series, "Oruchuban (Ebichu)"). However, when the series was released on video and DVD the name "Yebisu" was restored. Subsequent airing of the series in syndication (i.e. on Adult Swim in North America) tend to be based on video or DVD releases, so "Yebisu" was also seen when aired on such channels as well. Probably because of this legal battle, in Episode 10 and Episode 12, Misato switches from Yebisu brand beer to "Boa" brand beer.