Getting To Le Puy-en-Velay
Landing in Paris
I highly recommend taking a day or two in Paris to acclimatize to the time difference and figure out any last minute to-dos.
From CDG: Take the RER(B) blue line straight into Paris. They will charge you €9 for a special 'airport' metro ticket. You may need to change lines depending on where your hotel is located, but the system is all connected!
From Paris to Le Puy en Valey
You can take the train straight from Paris to Le Puy en Velay, or you can combine your train with a short bus ride to make it cheaper. I took a Ouibus bus from Paris to Lyon for €29 (book in advance for fares down to €15), then a SNCF train to Le Puy for €18.60. A direct train would have cost €100.
Rome2rio is a great resource for figuring out different route options, especially with smaller transportation services.
Transportation along the Camino
Bag too heavy? Sprain your ankle? Sometimes pilgrims need a break. Use these services to travel ahead or send your bags on without you: Compostel Bus (available between Le Puy - Conques) and Transports Claudine (Available between Conques - St. Jean). They take people and bags only to towns along the route, and usually only moving in the direction of St-Jean. Both services will need to be booked at least one day before. Make sure you know for sure where you're planning to end up before sending your bags. After booking, place your bags just inside the front door of your hostel before bed (unless otherwise instructed by your host). The driver usually comes very early in the morning and will not wait for you if the bag isn't ready. Make sure your name is clearly indicated.
I found Transports Claudine to be frustrating and rude over the phone. If you're not 100% fluent in French I would suggest asking your host or the local tourism office for help booking.
Getting back to Paris
From Conques (10 day adventure)
If you plan on returning to Paris from Conques, you can book a bus ticket online with Compostel'Bus back to Le Puy, then a train to Paris. I strongly suggest talking to someone at the Conques tourism office (right as you enter Conques along the Camino route) for help planning your transit. The bus does not always come unless the office calls them.
From Saint Jean Pied de Port (Full route)
Your best option is booking a train with SNCF from Saint Jean Pied de Port back to Paris, totalling about 7+ hours of travel. You may have to change trains in Bayonne, so read your ticket carefully or have someone bilingual take a look. If you can't get a good time or deal with SNCF, try searching for other routes on Rome2rio, and check with other pilgrims!
It's a good idea to get a phone plan for reservations, maps and emergencies. There are two good options for monthly no-contract SIM cards: Orange and Free Mobile. Orange has the cheapest option if you only plan on making calls to French numbers. Free Mobile offers a pretty amazing deal (€20) for unlimited international calls and data (double check that your country is included) if you plan on phoning home. The Free Mobile store in Paris is located here.