Hether, have you looked at the Free Checklist in this forum yet?
You really can fit all you need in one little backpack (maybe just change some of your needs[]), but sharing with your friend is a great idea. Your itinerary looks good; enjoy the coast from Barcelona up to Nice.
Not sure you need 3 days in Naples, maybe you could see some of the Amalfi coast while in that area.

I would pack enough clothes to get you through 7-10 days.  You will have to take your clothes to a laundromat.  However, if you pack lightweight clothes (clothes made of thin knits or synthetic fabric) as I suggest in my travel clothes guidelines you could always launder clothes in your sink which can save you some time and money(European laundromats can get pricey). 

It’s a good idea if all the clothes you pack can mix and match easily, this will give you lots of options.  Simple nuetral basics are easy to combine.

Versatile clothes will also stretch your wardrobe and keep you from packing a ton of clothes.  I’ve become a big fan of dresses, they are lightweight and can be layered over jeans, tights, or leggings.  Traveling in the summer, I would definetely recommend bringing a dress/skirts as Europeans don’t really wear shorts.  In my recent travels, I’ve noticed girls in Paris are still very much wearing leggings and the dress and slouchy boot look is also popular. 

Fitted clothing will help you fit in.  Please, please do not pack/wear big, baggy sweatshirts- I can spot American students in Europe from a mile away by their sweatshirts.

If you’re more of a casual gal, skinny jeans and trainers/ballet flats are also a popular look in Paris-this is also a comfortable outfit to accomodate all the walking you’ll be doing.  Pair this with a fitted simple tee or a cute top.  The hoodie look is somewhat popular in Europe as well.

Accessories such as scarves can also help stretch your wardrobe. 

A good walking sandal is also essential.  In Italy the girls are wearing this style of sandal which is very comfortable for walking.  Birkenstock makes this style.
[image]http://ecx.images-amazon.com/images/I/21fUdqS1oxL.AA160.jpg[/image]
Since you will be traveling after your studies a backpack is the way to go.  You can apply my packing light tips to see if that helps. 

Once you arrive in Paris, you can always buy a few things to spruce up your wardrobe.  H&M is a great store for cheap, trendy items.

Enjoy your trip!

Thanks for the advice. I figured a backpack was probably the way to go since I’ll be moving around a lot… Any recomendations on backpacks? I’ve been looking around the internet but I haven’t actually gone to stores to try any on. I’m pretty short (5’3”) so I think I will need something that is built for smaller people…

I did a search and came up with this thread on backpacks for shorter females.
link
I’ve had an Eagle Creek for several years now, I think maybe 7, and have been very happy with it. I’m not short, but mine is a smaller, easily adjustable pack.
Maybe you can get something during the post-holiday sales?

Thank you! That is very helpful.. Just curious…. does anyone ever use packing envelopes? I saw them on REI and the look like they would hold a lot a keep clothes from getting wrinkles in a small bag….