Insurance

You can get all insurance in France, but it’s possible that you, or your family, already have one. So you don’t have to pay for nothing, check if you’re already covered and get a certificate written in English or in French. ATOSIM students benefit from a cover that’s included in their program.
You’ll need a public liability (responsabilité civile) insurance, which covers a part of your expenses if you cause harm to someone. Its price is minimal.
If a insurance for individual accidents is technically only necessary if you’re doing an internship, fieldwork, or lab work, it is still recommended, and its price is minimal.
If you´re living in the residence, you’ll need to give a housing insurance certificate, in English or in French, in the two weeks following your arrival (otherwise, you run the risk of expulsion). Housing insurance covers you in case of fire, inundations, or explosion, and must necessarily mention this. In France, it costs around 50€ for a year and includes public liability insurance.
We also recommend you to get a private medical insurance, since you’ll only get here the basic cover. Check in your country to see if you’re covered when you’re abroad; if not, get a travel insurance. 

Housing

Rooms in the residence come with some furniture included : chairs, a desk, and shelves. They all have a fridge and hotplates, but no oven. A pillow and a cover are also provided, but no other bedding, so don’t forget to bring your bedsheets (and your duvet). As a side note, pillows in France are usually square-shaped and larger than what you might be used to. There is a laundry room inside the residence.
No dishes are provided; sometimes, some students who leave the residence also leave dishes behind, but this is not guaranteed. 
Most of the residence has central heating, meaning that radiators won’t necessarily work the very first days of cold weather, so remember to bring warm clothes! 
As for other equipment, the only lamp in the room is a ceiling light, there are no desk lamps. There is a vacuum cleaner, but it is shared between 4 to 7 apartments. There’s no carpet anyway, so a mop and a floorcloth will be enough.
High speed Internet is available in the rooms. To use it with your personal computer, you’ll have to use an Ethernet cable (RJ-45). If you have one, bring it; and if you don’t, you can borrow one (the number is limited though), or buy one near the school.
French electrical outlets are different from other countries. Bring an adapter if necessary!
Link to the officials informations about housing of ENS (French) 

What about the money?

At the beginning of the year, you´ll have quite a few expenses so be sure to plan ahead !
If you’re living in the residence, you must pay a deposit that’s the same amount as one month of rent, in addition to the first month of rent. The deposit will be paid back to you two months after your departure from the residence, if no damage has been observed. In the science campus, for F1bis-type rooms, you’ll then pay 380€ (twice 190€, correct price for the 2007-2008 year). You should add to this around 50€ for yearly housing insurance.
You’ll have to pay, no matter what your status is, 4€70 in ‘preventive medicine expenses’ (« frais de médecine préventive ») (this allows you to go see the school nurse).
Depending on your status, you may have to pay tuition, which cost around 200€ depending on your year. Erasmus students are not affected by this.
Non-European students will probably have to sign up for Social Security, which costs around 186€ per year.
Signing up with the Bureau des Elèves (giving you access to clubs among other benefits) will cost you 30€, and signing up with the sports association (Association Sportive) will be 22€. If you want to participate in the Week-End d’Intégration, the fee is 150€ (you must be a member of the BDE to participate), and a deposit of € will be required, that will be paid back to you after the WeI.
If you’re planning to eat at the Restaurant Universitaire, each meal will cost you 2€75.
Also plan enough money to live decently until your French bank account has been set up (it can take 1-2 weeks to receive your card and checkbook if you have asked for one).
According to European legislation, if you’re part of the Euro zone, your bank cannot charge you more to use your card (for example Visa, Mastercard, …) in France than in your country. So it is not really necessary to come with a lot of cash. Remember to check how much your bank will charge you if you use your card in France. In any case, it’s always a good idea to have a few euros in cash on you. 
 
Don’t forget to follow the instruction that ENS gives you !