As seen in the movie, The Beatles are given "uppers" pills so they can keep performing when they're getting tired. Also, as seen in the shot after John accepts the pills for the first time, the Beatles are performing "Long Tall Sally" like crazed maniacs with eyes bulging and sweating profusely. The reason for this is that the uppers were actually prescription strength speed pills. According to all of the Beatles in various interviews (most prominently in the "Beatles Anthology" film and book), the band was forced to perform up to 8 hours a night, far and away more than a band can possibly play given the normal fatigue that sets in from singing and playing. Whenever they grew tired, the bartenders or the waitresses would often give the Beatles (and other performers) uppers to keep them going. Because of this, and their horrible living conditions in the Kaiserkeller Club's back room, the Beatles were often sweaty, smelly, pale, and shockingly thin (speed pills back then doubled as diet pills) because they rarely bathed, hardly ever washed their clothes, or more importantly, ate healthy meals. However, after Stuart Sutcliffe began dating Astrid Kirchherr, she would feed the band and wash their clothes and allow them access to her bathroom for bathing. All of the Beatles have said that Astrid, more or less, kept them alive and healthy.
When Klaus Voormann introduces himself to the Beatles, he mentions that he's an artist, and lays a stack of album covers on the bar. Voorman would later go on to create the covers for The Beatles albums "Revolver" and "The Beatles Anthology" (One large painting cut into thirds for the three volumes).
1990s punk-rock musicians and techniques were used to create the film's soundtrack, instead of the precise styles of the period, to better convey the way the music felt to the early Beatles audiences; "it was the punk of its day". Ringo Starr has been quoted as saying that the movie's music reflects exactly the punk band that the Beatles were back then.
The soundtrack does not feature any Lennon-McCartney compositions, presumably for budgetary reasons. However, the film does include many songs covered by the Beatles as part of their well-known Hamburg/Cavern Club repertoire. Among these are "Twist and Shout" (later to appear on their debut album "Please Please Me") and "Long Tall Sally" (later released on an EP of the same name).
The only appearance of Ringo Starr in the film, laying sick on Stuart's bed, is not the only encounter that the Beatles had with the man who would eventually become their drummer. In reality, they had known Ringo back in Liverpool and he was apart of the Beatles' chief rivals Rory Storm & The Hurricanes (which many have said was a superior band to the Beatles at the time). They even hung out with Ringo in Hamburg and he sat in on jam sessions late at night when the club was nearly empty. Their time spent together in Hamburg would actually start the ball rolling on Ringo replacing Pete Best as the drummer.
Stephen Dorff was the only actor of the group who could actually play his instrument (he's actually a professional musician). Ironically, his character, Stuart Sutcliffe, could not play his instrument, which is one of the chief reasons the real Paul McCartney later cited for wanting Stuart out of the band. In the screenplay, however, the McCartney character agrees with Lennon that Stuart is a great bassist, and objects only to his stiff manner on stage.
In his interview for the Beatles Anthology book, Paul McCartney states that his only objection to the film was that John Lennon is shown singing "Long Tall Sally" when that was really Paul's own signature song. Paul even sings the song for the single release with "I Feel Fine".
During the montage of the Beatles performing at the club, there is inter-cutting of strippers performing on the stage. The Beatles often alternated their performances with other bands and strippers. In many accounts of the Beatles' days in Hamburg, it's said that not only were there female strippers, but there were transvestite strippers as well.
The trivia item below may give away important plot points.
In the film, the Beatles are deported because George Harrison is caught working in nightclubs while underage, in violation of his work visa. In reality, George was deported for that reason, but Paul McCartney and Pete Best were deported for "committing arson" when they pinned a condom on the wall of the Kaiserkeller Club and set it on fire as a joke. John Lennon was the only one who was not deported (besides Stuart Sutcliffe, who had already left the band and was living with Astrid). Technically, John could have stayed behind, but in various interviews he stated that he accompanied the others back to England because, in his words: "They were my friends and my band mates. What the fuck else could I do?"