I'm currently in my 20's and my absolute must have jewelry pieces are:
1. White gold and diamond huggie earrings. I prefer these to diamond studs, as they don't hurt me ears. Mine were a 21st birthday gift.
2. A wear every day necklace. I don't have one of these at the moment as my tastes have changed from yellow to white gold, I am looking to get a white gold and diamond solitaire pendant later this year.
3. A good strand of pearls - this is for me mind you. I know plenty of 20 year olds who wouldn't be caught dead in sensible pearls, or simple don't see the appeal. I was lucky enough to inherit mine, when my mum realized she never wore it, after she was given them by my grandmother - who also never wore them. These were originally my great grandmothers, bought for her by her son during WW2 when he served in Japan. They have recently been restrung (as my great grandmother was very petite she wore it in a triple string, but now its a single opera length strand) to be more versatile. While not something most 20 years olds could afford I adore them.
4. A lovely classic ring - also something I don't own yet. Unfortunately I have very expensive tastes so my ideal ring is currently not in the budget. With an unlimited budget I would have an exact copy of my grandmothers ring made, which is a raised cluster ring set with diamonds around a Ceylon sapphire.
5. A beautiful watch - I'm lucky enough to own a Hermes Kelly lock watch, which is my absolute favorite and I truly believe it doubles as jewelry.
I think these 5 are good staples, for me at least, but of course every girl has got to have her stand out pieces which she only wears every now and then.
These are really great!