I use a mailbox mod, so no drips get on the chips.
When I'm finished smoking, I move the unburned pellets away from those that are burning and let the tray burn out overnight in the external smoker. Our neighbor's house burned down thirty years ago when he threw the "ashes" from his fireplace into the trash, which was kept in the garage, so I'm really paranoid about throwing out anything that was once on fire.
I then save the unburned pellets. If there are a few charred pellets mixed in, I don't obsess about them, and let them come along for the next party. They'll burn just fine and will taste just the same.