Well I did promise, so here's an expanded take on Jakaru's original guide to buying milk - now with photos!
(update from 2024 - sorry about the Photobucket banners on some of the pictures; unfortunately I've lost some of the originals and these are the best I could recover. I've also added a few notes where things might have changed since this post was originally written in 2012)
First things first, get yourself to the station between
Disneyland Park and the Village. This is the station entrance on the park side that is nearer the RER platforms (while the Village entrance is nearer the TGV/Eurostar platforms), but it doesn't matter which side you go in as you can walk between them.
Straight ahead you'll find a bank of ticket machines - you want to go to the green ones.
(note - the photo I originally took has been deleted, so this is a borrowed photo from someone else's blog)
You need to use the big grey scroll wheel on the machine to choose "Acheter les tickets" and then on the second page, you can choose English language and everything is a lot easier from there!
(update - the ticket machines should all be touch screen nowadays and a lot easier to change languages)
Now as far as I could see, there were no options for return tickets, only one-way, so choose Marne-la-Vallée - Chessy as your departure station and Val D'Europe as your destination. I have a feeling it was ~1.60 per ticket, but unfortunately I can't remember exactly and the RATP.fr website only gives you prices to stations from the centre of Paris!
(update - ticket prices have obviously gone up since this post - as of 2024 a single is 2.20)
Anyway, your ticket should look like this:
Follow these signs:
And you'll end up at these gates (there's actually a set of gates on both sides of you - it doesn't matter which ones you take as you end up on the same platform). Put your ticket in the gate and pass through.
Go down the escalator to the platform.
Now you can look at a map if you want, but there's no real need as we're only going one stop.
There are overhead displays showing you what stations the next train to arrive will be stopping at, but all trains are going to stop at Val D'Europe, so don't worry.
Board the first train that arrives, if there isn't already one waiting, which there might well be, considering we're at the end of the line here.
And just in case you forget what the inside of a train looks like... (not the only stare I got from someone wondering why the heck I was taking photos of the most mundane things!)
About three minutes later, you will arrive at Val D'Europe station, so exit on to the platform and look for the signs.
We want Exit (Sortie) number 1, which is helpfully signposted for "Centre commercial" as well, which is where we're going, so bear left. You can either go up the stairs, or take the lift just behind them to get up to the station concourse level.
Once on the upper level, pass through the gates as before.
You'll get your ticket back, but it's not longer any use to you so you can discard it in the bin - you'll need to buy another one for the return journey.
Head out of the main doors on to the street and you'll be faced with this view.
You want to turn right and head towards the shopping centre, although it's not obvious that it's there if you haven't been there before (and there's no signs that I could see). Can you see the glass dome poking out from the side of the tree? That's where you are going.
After walking past a number of shops, you'll come to a T-junction that you need to cross. I have no idea if this is a proper pedestrian crossing or not, but everyone was walking straight out in front of cars and they were stopping, so I say just go for it!
(update - there are now pedestrian crossing lights at this junction, but people still cross whenever they want!)
And now you get your first glimpse of the centre itself, with your entrance helpfully being labelled "Passage de la Gare", so at least you'll know what door to head out of when going back to the station.
Here's the view once you get inside the centre:
Now the Auchan hypermarket is on two levels, but the food section is on the lower level (the upper level is clothes, homewares, DIY stuff etc.), so I'd suggest you either go down the stairs straight in front of you, or head down the corridor on the left of this photo, which leads to:
...a set of escalators/travelators going down to exactly the same place. The set going down is the one on the far side by the way. Whichever you choose, you'll end up here, with Auchan on the left:
Keep on walking to the far end to find the main entrance (I think there are a number of ways in, but it's easier to navigate the store from this point and you've got more chance of finding a basket here).
I took a photo here and almost got in trouble with a security guard! "Pas de photo monsieur!". I quickly remembered "désolé!" from my French GCSE and put my camera away and he seemed happy, then got round the corner and took it out and started snapping away again! Anyway, here's the shot that nearly got me thrown in French prison or something (the story sounds better if I make it sound worse!)
Go straight ahead and head to the back of the store. By all means, meander through the aisles looking at all the wonderful stuff, but as this guide is purely about milk, I'm heading straight there and going back for everything else later!
On the back wall, you should very quickly find this section:
This is the UHT milk section we all know and dislike. The good news is the fresh milk is just behind us (and slightly to the left). Turn around and hopefully you should see this aisle:
It's the first section on the aisle we're interested in (where all the red and blue capped bottles are). A close-up shot:
We bought a number of brands to test, but below are the ones we settled on as being the nearest to British milk. Neither of them tasted precisely the same when drunk alone (although not bad), but when in cereal or in tea, or consumed while eating my morning croissants, it was very hard to tell any difference, and there certainly was no after taste.
(update - these brands of milk may not be available now, but anything with "frais" in the name should be good)
Semi-skimmed (2% fat) = Demi-Ecreme / blue lid. Full-fat (4%) = Entier / red lid.
Unfortunately, there was no skimmed (0.1% / fat free) alternative in fresh milk that was palatable, though my wife (who is the skimmed milk drinker) did say that she thought the semi skimmed wasn't quite as creamy as British versions, so it was acceptable for her.
After that, you're on your own to pay for your groceries and exit the store. Having already had my run-in with authority, I wasn't about to take pictures of the checkouts!
(update - there are now a large bank of self-checkouts available, which may be easier for you)
Back to the station, buy a ticket to "Marne-la-Vallée - Chessy" and remember to go to the opposite platform to catch the train this time - this one has an escalator down if that's any help in remembering the correct one!
And of course, make sure you take a trip to the ice machine at your hotel so that you can keep your milk cool for the morning. The first day, I did sneak the bottle into breakfast in a bag, but I soon realised that nobody was bothered and just took it in openly for the rest of the holiday.
Have fun!