Ok,I am going to brainstorm, so might be garbage that comes out of the ol' noodle.:
Stirrup leather wraps, changeable browbands, bit warmers, "ouch" pad covers (for those things you chill and put on an ouwie), wild rags (large western style bandanas), hat bands, bit bags with pockets for each bit and can hang on a hook (like shoe bags?), Cell phone holders, hay carrier (like those things people used to use to carry an armload of logs to the fireplace and keep their arms clean)
I wonder if it would work to do like a duvet cover, for wester plain wool felt saddle pads. It would be really thin, so horse would still benefit primarily from tthe good wool, but would keep grime off and add pzazz.
Ok, my noodle is soggy, time to wathc some tele and go to bed.