Continuity mistake: When Brad gets to his grandma's house he is standing outside her window. He holds his bag in his left hand and switches it to his right. When it cuts, he switches again. (00:10:00)
Continuity mistake: At the end when Brad kisses Brenda he turns around and walks away. When it cuts, he does the same thing again. (01:17:30)
Answer: From what I recall, Charlie followed the bounty hunters as they walked away in the first film. So the implication is that they decided to let him tag along with them. (And that makes sense. After all, he helped them destroy the Krites in the first film, so he'd be useful.)
TedStixon