A pair of strong shears and a hole punch. You will need rivets and the accompanying tool, which will also require a hammer. You could stitch it, this would dictate the use of waxed gut and a special needle, but I prefer the rivets for strength.
Bulk leather on-line will get you going on many projects as well, including sheaths (a good start) and holsters (something I will start up soon).
Tandy Leather Factory - Home