I ran across Pearlies in Mary Poppins when I was a kid, and sort of assumed they had died out around the same time as dancing chimney sweeps. I was thus somewhat surprised to find this description of modern Pearlies and learn that the tradition is alive and well.
Pearlies (you can read about their history at the links above) wear clothing decorated with pearl buttons sewn in elaborate patterns. If you’ve got a stash of castoff buttons, this would be a great use for them.
Although a full suit or dress covered with buttons would certainly be an impressive–not to mention heavy–sight, smaller projects such as a hat, tote bag, or throw pillow decorated with a traditional pattern might be rather less daunting. A Pearly outfit or accessory would be an interesting choice for a Steampunk costume as well.
You can find historic patterns at sites devoted to the tradition* (search “pearly kings and queens” or “pearlies of London”), but could also adapt simple cross-stitch designs such as skulls or spiders for something a bit darker.
If you’re like me, you probably already have a box of random buttons lurking somewhere. If not, look for them in thrift stores or ask crafty friends to share their stash. As a last resort, plain plastic buttons can be purchased fairly cheaply at fabric or craft stores. (If you plan to use a whole lot of them, look into buying them wholesale instead; many manufacturers have a minimum wholesale order of only $50 or so.)
Since there’s a lot of hand-sewing involved (I suppose you could try hot glue for lightly-used items like neckties, but would make no promises about durability) this is a good project if you like to keep your hands busy whilst watching TV. You could start small, perhaps something as simple as a button brooch, and then expand into larger and more elaborate projects as you gain experience. The results are certainly attractive and unique.
*Since Pearlies in the UK are associated with charitable organizations, I have no idea whether wearing an “unauthorized” costume there will get you glared at or not. Um, beware, I guess.