You will need the following:
Potting soil bags, for this short dress, I needed about four bags, you may need more or less depending upon the style, length, and size of your dress.
Fasteners: I used velcro, but you can use a zipper, snaps, corset lacing and grommets, etc. Make it fit to your dress.
Scissors or a rotary cutter (Note, do NOT use your nice fabric scissors on these, it will ruin your scissors, use general ones.)
Sewing machine or alot of patience. For a no sew version you can use duct tape, but I can't promise it will hold together very well, so make sure you wear something under it if you go that route.
Soap and water, these bags come with dirt in them. Dirt is dirty, you should wash said bags before hand, rather then get dirt all over your house.
Electrical, duct, or bias tape. In coordinating colors! That or you can roll your hems, but who has that kind of time?