Things I don't wear every day, but get pulled out for many occasions:
Silk blouse (works for any vaguely smart work thing, also great for evening out, effortlessly cool and polished. Mine's from Massimo Dutti about 8 years old).
Denim jacket (mine's from TopShop, about 15 years old)
Leather biker (Whistles bought in sale, about 4 years old)
Black dress for funerals (8 years old, Banana Republic, thankfully only required a few times)
Loafers (when I need to look smart for work - I usually wear trainers - these come out. Russell & Bromley 5 years ish)
Pleather jeans (New Look about 3 years), always makes an evening outfit cooler (works well with silk blouse above).
Grey suede heeled boots (Pierre Hardy for Gap, about 10 years old). Will never get rid of these, every time I wear them people ask me where they're from.
None of these items get worn very much (unlike my uniform of jeans, Ts, trainers, cashmere jumpers in winter and blazers), but they'll never leave my wardrobe.