Very interesting replies. I'll play Jamie's game based on my own highland experience of highland dance if you don't mind since almost all of the items are used (except sporran).

item of the very finest quality (bespoke to your specifications)

The jacket. Absolutely, this. A low quality jacket can be spotted a mile away, an average jacket blends in, but a high quality well-fitted jacket is a stand-out.

item of very good quality.

Tartan hose. A highland dancer's hose is made from lace weight wool yarn and quality shows here.

item of good quality

The kilt. Why third? Because there are only a handful of tartan weavers, all of which do top quality fabrics. There is no second best for them. And an average kilt still swings the same as top quality one. I should know, I've made my own and don't rank myself very high in the kiltmakers rank, yet I've gotten many compliments on the kilt, both construction wise and swingedge factor when dancing. (either I'm better than I thought or people are just being nice to me -probably the latter)

item of average quality

dance slippers or ghillies. This one really hurts. Literally. I love my Hullachans. In fact, I may have to interchange with the kilt. It might cost more in the long run in physio fees if I don't.

item of low quality

Female dancers don't wear sporrans, in fact, just the four items above complete her. I suppose I could add in the dickie here though. As long as there's a strip of lace showing at the neckline, we're done.