answer: Barbara agrees to cover for Sam because he wants to buy Father's Day gift. Barbara asks him to buy a gift for her father too and suggests a couple of ties.
documents: #Person1#: Barbara, could you cover for me for a few hours?
  #Person2#: I guess so, Sam. I could tell the boss you've gone to buy some office supplies if she asks.
  #Person1#: Thanks, I owe you one.
  #Person2#: Hey, not so fast, Mister. I need to know where you're going. Why do you need to be gone for that long?
  #Person1#: I forgot to get my dad something for Father's Day.
  #Person2#: Oh, man! You forgot your own dad's birthday?
  #Person1#: No, it's not his birthday. It's Father's Day!
  #Person2#: Since you're going, would you mind picking up something for my dad too?
  #Person1#: Oh, well, I guess I don't really know your dad though. Do I?
  #Person2#: Couldn't you just buy a couple of ties in the shop downstairs? That would be easy enough, and that way you could come back before Mrs. Greenway checks on us.
  #Person1#: OK, good idea. I'll be back in 30 minutes then.