Go to convention and talk with Mel. He's sick and wants some coffee.
Talk with the vendor - he has cup of coffee, but doesn't want to give it to Randal. Go outside and tell Murray that Mel is sick because of bad hot dog.
Go inside and go to the occupied latrine (on the back). Talk with Mel, go to the main hall and have a conversation with Murray. Give him the rotten hot dog .
Again talk with Mel, go to the main hall and take coffee. Give it to Mel.
Randal sells the miniature. Go to Charlie, he will sell you the ring if Randal give him Captain Red figure.
Before you leave open the package from the boss. Give shirt to the guy dressed up like Darth Vader, he'll give you eucalyptus candy. The second shirt give to nerd who is dressed like a Superman. You'll receive a fishing rod.
Go to exit, when someone dressed like Doc from Back to the Future gives you a plutonium rod.