I am always going and coming to work in Paris for 2-3 months at a time. Here's what's currently in my closet at my flat.
(note that I am 26 and work at a multi-national company in the fashion industry)

1. Black pumps (I can walk miles in them)
2. Athletic imspired shoes.
3. Flip flops
4. 10 pairs of undies
5. 5 bras
6. socks (about 6 pairs)
7. Red pumps that I can also walk in
8. Black dress that if I put a suit jacket over I can wear to work.
9. 4 suits in various colors
10. EU rolly bag
11. overnight bag
12. 3 sweaters (black)
13. Winter coat
14. an assortment of work out clothes, tanks and such
15. 1 swim suit


Obviously I have some random shirts and such that I have here just b/c I live here, but that's the basics that I keep here. I rarely travel back to the US with anything other than what I am wearing, my purse and my laptop so I would like to think that I've been rather good at having the basics here.