Halloween Bugs Me (Ghosts of Fear Street #25) R.L. Stine

Trick, or....TRICK? Greg Dreamer is sick of Paul Boyd's stupid bragging. Everything is competition to Paul. Who can throw farther, who can burp louder - everything! And the worst thing is...Paul always wins. 

But not this time. Even though he says he'll get more Halloween candy than Greg, Greg is going to beat him. Because Greg has a secret weapon. It looks like a plain old bag, but when you put something in it, the bag makes more candy. More money. More cats. Even more bugs! 

And one thing Greg hadn't counted on. More trouble.