The basic idea behind this project is that you want to put a metal plate with some casters on it onto your bag. You'll want the plate to make sure the casters are properly aligned and to provide stability. Otherwise, the casters might just push into the luggage, and then you'd just be dragging your bag across the floor. Not cool.
For this project, you'll need the following things -
Wheels - I'm using some hardwares store casters. You may want to pick the rubber ones, since
they're probably quieter, but I really dug the look of the solid iron ones.
Metal Plate - Or really any flat, solid, hard material. You could use wood, or plexiglass. I'm using aluminum, since it won't rust, is nice and shiny, and I got this piece for free.
Marker - For Marking!
Nuts and Bolts - Otherwise, the plate and wheels will fall off.
Grommeting kit - This will help you reinforce the holes you put in your bag, so the plate won't fall off either.
Luggage - This project is really hard to do without this.