There are a few things that I believe every girl should have in their closet. You don't have to spend thousands of dollars on these however, it truly helps to have them in your wardrobe. There are also many other things that should be included in your closet and these are just a few.
1. Navy Sweater- it can be any cut or style as long as its navy. Navy goes with pretty much everything and if you invest in a great one, either cashmere or cotton, then it should last you forever. I suggest J.Crew's Tippi sweater: http://www.jcrew.com/womens_category/sweaters/crewnecksandvnecks/PRDOVR~46725/46725.jsp
2. Dark wash jeans that fit right- Dark wash jeans are crucial, you can dress them up or dress them down. Before you invest in an expensive pair make sure you love them and that they are comfortable. As for style, I recommend skinny fit or straight leg. Don't go with anything too trendy like 'boyfriend-fit' or 'super-flared'. Above all, go with what you love and what looks best on you. My favorite pair of jeans are a pair of super skinny jeans from Joe's Jeans. There is a little bit of stretch but they aren't too much like leggings.
3. Leather Boots- depending on your personal style you can decide whether to get black or brown, and if you can afford it, get both or get one now and the other later. I definitely recommend getting real leather because they look better and last longer. Go for a more classic style, something that isn't too trendy. A good pair of leather boots will last you forever and they don't have to be from a major brand. If you're seeking out an authentic pair of riding boots than go to an equestrian shop for a real pair of riding boots. My favorite pair of boots is from J.Crew (surprise, surprise) but I love them; they look and fit wonderfully.
4. White Jeans- White jeans, like dark wash jeans, are crucial. Despite popular belief, with the right styling you can wear white jeans in the winter and the summer. My favorite way to wear white jeans in the winter is with my tall brown leather boots and a navy, or other dark colored sweater with a leather jacket or peacoat. In the summer, I pair my white jeans with espadrilles and a very feminine summery top or a looser linen blouse. Just like dark wash jeans, white jeans can be dressed up or dressed down. When investing in a pair of white jeans go with what looks best on you, what you feel comfortable in. Personally I like skinny fit but if you want to wear straight legs then all the power to you.
5. Leather Jacket- Leather jackets are a little trickier, at least from my experiences, it takes a little searching to find the perfect leather jacket, and it doesn't have to be from a major department store. Once you find your perfect leather jacket I would buy it as soon as you can because it will last you a lifetime. Wear it as much as possible so you get that broken-in and more casual look (if thats the style you're going for) I prefer brown to black, however go with what suits your style better. Avoid things that are too trendy, classic is better. Buy the jacket that looks the best on you not the one that you saw in Vogue the other day.
Without going into too much more detail a few other things I would invest in are a white tank (in my opinion, Abercrombie and Fitch have the best tanks), a navy blazer (J.Crew as some really great ones, and don't go with anything too trendy and make sure to get one that fits right!), and a men's watch (Michael Kors has some great ones however if you want an authentic men's watch, buy one from the men's side of the department store or where ever you are buying the watch.) The most obvious staple of all is The Little Black Dress like every other staple I mentioned, go with what looks great and will last forever. Don't pick one that is too trendy. As for shoes, black patent leather pumps and nude patent leather pumps are great things to invest in and if you buy the right pair they should last you forever.