Revealing mistake: Near the end when everyone is trying to escape the building before the explosion, the team escapes but Sam is missing. Michael calls out for Sam until he is shouting. A view of the building shows a stack of something with a horizontal gap in the middle. Sam's arm and blue shirt can be seen in the gap while Bruce Campbell waits for his cue to come out with the hostage.
Continuity mistake: Michael attempts to have a conversation with his mother Maddie while she is folding clothes. She picks up a blue Hawaiian shirt and begins to fold it. The angle switches for a moment to Michael and then immediately back to Maddie, only now she is folding a white shirt. The blue shirt is already folded on the table and is seen under another shirt. (00:11:00 - 00:11:30)
Chosen answer: It might not actually have one, in which case, he'd have to go down into the club and use theirs. As for showering, going to his mother's house or a gym membership would take care of that.
Captain Defenestrator