-A patch of cowhide or deer skin folded in half with a plastic pick inside. Glue together and trim. This gives a funky muffled sound
-Several scraps of stiff plastic sheet, not too stiff, maybe cut from the lid of a pie container. Here in Colorado, pies come in a pie pan, inside a clear plastic clamshell-like container. I don't know how they come in the UK. Anyway, I cut several pieces about oh, 3 x 1.5 cm and round off one end. The other ends I slide into cuts in a little block of wood and glue them there. Now I have a nifty multipick. Makes a lot of clackity noise on the strings.
-Next comes a simple brush, the kind draftsmen used to use on a drafting board to brush off eraser crumbs. I use this on a 12-string. It makes a sound reminiscent of wind in the rigging. You could experiment with different brushes, and even cut some of the whiskers out to get different effects (not your mother's favorite brush tho)
-with any simple plastic pick, my clumsy fingers will probly drop it, so I drill a hole and thread a little string loop that goes around my finger. So I'm not scrambling around looking for it bent over with my butt toward the audience.