Yes !
Carpooling is a very nice way to travel, but the very website that started the trend covoiturage.fr is no longer free and i dont know if it will still remain as cheap and easy as it was.
Buying train tickets in advance can help you save a lot of money, with the Prems program of SNCF. But when you cant use your tickets, or you didnt buy your tickets early enough (2, or 3 months) you can still buy/sell it on specialized websites like trocdesprems. One day, I bought an eurostar round trip Paris/London 2 weeks in advance for 65 euros there. Rather cheap. The difficulty is that you have to make an appointment and meet the seller / buyer somewhere, which can be tricky.
Hitchhinking is still possible, and is working okay outside paris if you look neat enough to reassure drivers.
Good luck