The short answer is: as little as possible!

A few quick thoughts:

• You can get anything in Paris.
  
• Many things will be provided where you stay.
  
• No one will notice if you wore that outfit already this week. 
  
• Pack your suit cases. Then take a third of it away. Do it again.
  
• Test everything before you go.
  

I must admit that I've learned much of this THE HARD WAY!

Remember, you can get anything in Paris.

PERSONAL ITEMS
Only bring a couple day's supply of shampoo, soap, body wash, etc. I do suggest bringing toothpaste as fluoride toothpaste is only available in pharmacies - a bit pricey.

The tap water is highly mineralized (hard) in France and so I think it's better to buy locally formulated products. Besides, shampoo and other items like body wash, soap, etc.  are heavy and can leak in your suit case. Remember, airline regulations allow only small amounts of these liquids in your carry-on items. Fortunately, the travel sized toothpaste is enough for a week or two. I would also buy shaving cream, razors, and feminine products when you get there. It can, however, be a tricky balance between buying it here (probably cheaper), or packing lightly and getting it there.

Leave home without towels. They are very bulky and are often supplied, but be sure to check ahead of time with your accommodations to be sure. I've even bought towels when my husband and I stayed in the $35/night hotel and then left them behind.

Hair dryers and clothes irons are also are supplied in most accommodations. Leaving them at home simplifies the special voltage and plug adapters you'd need. But, if Paris is only one of your stops, you may want to carry bring these items with the appropriate adapters.

CLOTHES
No one will notice if you wore that outfit already this week!

No matter how often I travel, I still over pack. My advice is to find your 3 favorite outfits - the ones you are most comfortable wearing. Black is always appropriate, jeans are accepted at most places. Peoples' dress is formal, casual, and everywhere in between.

Women may want to have a skirt just in case, as some religious sites or really nice restaurants may require it. If you rent an apartment, you will likely have a washer so you can do your laundry as you need to.

The other advantage to packing few clothes - you'll have more room for buying new ones! Just beware the sticker shock. Unless you are from a large city already, you may cough up a hair ball when you see the prices in most stores!! There are, however, bargains to be had - more on that later!

Style tip:
Although the French and the millions of other people you'll see on the streets are not always dressed in Yves St. Laurent and expensive suits, their casual is more dressy than American casual. T-shirts, torn jeans and sweats are rarely seen. The French dresses nicely, neatly, and with a sense of style. 

I mention this because dressing more like the locals will help you to look less like a tourist and so less like a target for pick-pockets. You may also find that the French may treat you more respectfully, than if you are dress as you do at home.
 
SHOES
If you can manage two pair, that's great. Men will probably be able to do this, women may have a little harder time.

Whatever you do wear, I recommend you try wearing them A LOT before you go. Get your blisters at home.

Although there are still women who wear the famous high heels across the cobble stone streets of Paris, this younger generation has decided to forgo the regular trips to the podiatrist that their mothers endured and wear more sensible shoes. Three years ago, I saw a sight I thought I'd never see: many French women wearing Birkenstocks and other comfortable, good-for-your-feet shoes!

Comfortable shoes have become more stylish - you CAN find "sensible" shoes without without the ugly factor!

LUGGAGE
Luggage has come a long way. All I can say it, "Yea wheels!!"

That being said, the most comfortable bag I ever carried was a frame pack while I traveled around Europe with my Eurail Pass and one of Rick Steves' first guide books!

That was great after college, but it has never really been practical since. But I have used some amazing backpacks as carry on. They allowed me to more ergonomically carry my stuff, and have two hands free. I was packing light!

On our last trip, we all had one back pack and one rolling suit case and it worked well. I highly suggest, if your budget allows, pay extra for the 360 degree turning wheels if you choose rolling luggage.

Whatever you use, make sure you "test-drive" it. Under the cover of darkness, haul it around your neighborhood. At the very least, pack them and then carry them up and down and up and down your stairs and around your house. I know this seems funny, but remember you'll be schlepping it around the airport and other places. The luggage should match your physical abilities.

ELECTRONICS
There are more and more things to consider when traveling now. It used to be simple - a hair dryer, maybe an iron, and a camera. Now, in the internet/cell phone/digital camera age, there are more options. Read about electronics for your trip.

PACKING LIST
it's always a good idea to have a packing list to start with. For me, the excitement of the trip the and travel details can make me a little crazy, so the list helps focus me. Here's an example of my packing list.

My packing list

#7 Money matters