I took a leather crafting class at Workshop in San Francisco and made a leather harness to wear over tees and tanks this summer! It's a lot easier to work with leather than I thought. Just a few O-rings and studs (it's a good craft to work out some aggression, too!) and you can make just about any accessory.
Starting off, good leather scissors (or a rotary cutter) are key.
Pencils for sketching, and a good hole punch.
I started off with pre-cut leather strips which made the process a bit quicker.
My idea: a cross-body strap with a double wrap waist (plus beer for inspiration).
And also had enough time to make a choker and keychain from leftover scraps!