They resemble small duffle bags tied up. In the old/computer version of the game, they would make a small glow when far away in the dark making them easy to see.
When in the Halloween Mode, they are two suckers, a cupcake, and a donut since they're suppose to represent treats in Halloween.
The bag count is at the bottom of the game screen, shown like this:
Bags Collected / Bags Needed
Once the player collects the specified amount of bags, the player may access the steel door in front of the bedroom to finish the game. The player may collect more bags than the amount specified, but this will not avail anything whatsoever.
The more bags found, the more frequent the ghosts will be changing floors.
Trick or Treat Mode:
In this mode, they are all replaced with candies, and treats since it's Halloween themed. There are more than thirty that the player may get if they want.