Travelling from Grenoble
There are many options to go to and from Grenoble. To travel down there I took the Eurostar from London St. Pancreas to Paris (Gare du nord). Then you have to change to Gare du Lyon and then its straight down to Grenoble. Its one change (which you can easily take a taxi for less than 15€) and unlike a flight you can take what you want. I was able to bring a massive suitcase, a 70 litre backpack and a smaller suitcase (although still large). I’m not good at taking the minimum, so this way suited me. I think it cost around 65€ for the trains, all booked as one on the Eurostar website www.eurostar.com, and you get to experience the fast train from Paris to Grenoble. Do remember that you'll probably pick some stuff in Grenoble, like Ski gear, so think about that for the way back. Vacuum Packing is something to look into to keep stuff into as little bags as possible.
Otherwise, you can fly. Ryanair and Easyjet don't fly to Grenoble airport when it’s not ski season, so you have to go to Lyon or Geneva and take a train or bus. In the end, I think it becomes a lot easier to use Eurostar for the journey down. For Christmas and onwards, you can go from the very small Grenoble airport which is a 22€ return journey away from the train station by bus (about 40 minutes). Make sure you find out term dates and book as soon as the websites put up their flights (late September for Christmas I think, but keep checking). Sometimes you need to really ask for exam dates a few times because the small size of the department means that they think they can just organise exams when they want. For January exams, I had exams on the 3rd and 4th of January, so make sure you're back in time if you return home. Also take note that the airport will then again be closed by the end of the academic year.