During the Credits (spoilers)
There are flashes of The Collector dragging his steamer trunk down a hallway, along with each character’s fate shown.
After the Credits (spoilers)
The Collector is shown watching slides or home movies possibly at his next victim’s house and the camera pans down to show he is sitting on his steamer trunk. From inside the trunk we hear Arkin yell “I’m going to fucking kill you!” a couple times and the Collector gives the trunk a swift kick with his heel to shut Arkin up.
Special thanks to Mark B. for the stinger submission!