Well, I think everyone should try & own at least one full EI with a lot of variety (Gogh Reed, Compass, Zodiacal etc.) It's one way of having a lot to draw on and probably works out better value than buying that many outfits individually. You can buy a Gogh these days for as little as 600k & I still think it's just as nice as when it first came out, with a variety of fantasy type outfits & accessories, and one of my favourite wigs.
When it comes to gold-shop stuff, I think everyone should have some wool tops, and a good pair of glasses or two. Also, the Starter Boots. They come in brown, grey & charcoal & they're just a really nice shape.
But I mean judging by my personal taste, everyone should have Imaginary Friend and at least 3,425,746 rainbow items. I don't really expect people to do that. There's so many items these days, it's not like we all have to wear the same things.
Everyone has different styles, of course. But everyone should have a variety of small accessories for the finishing touches. Every avatar can benefit from the detail that accessories give you.
And the best part is, you don't have to spend much. Just head on over to Barton Jewelers and browse the selection. Necklaces, bracelets, hairpins, watches, circlets, crowns, anklets. There's a ton of stuff to choose from.
Sainte Ciel: Agape and Masquerade. The former for the scissors, it makes a lot of ugly hairs cute. The latter is very versatile, I'd recommend it to girls more just for the blush and mascara but guys can find it useful too.
I think everyone should have the gold/silver items. The lovely genie gold and silver sets can really finish an avatar at times, or they just add more flare to the avatar. But I also like the gold/silver sashes and belts.
Not an item per se, but we should be able to close our eyes without a stupid item. Just about every item that closes your eyes is super expensive. Also blush. What I'm using now is okay, but I don't like all the crap floating behind my avatar, and of course, items with blush are also super expensive.