Montpellier is a city in the South of France.
Apart from an attractive city in itself, it is situated next to a main highway A9/E15 connecting cities such as Perpignan and Barcelona to the South, Aix-en-Provence and Marseilles to the East, Lyon and Paris to the North, and Toulouse and Bourdeaux to the West.
For a few months, there has been a new tramway line in Montpellier, line 2, and it goes directly to a péage (toll plaza). Take tram number 2 at the train station, direction "Saint Jean de Vedas", then get out at the stop "Saint Jean le Sec". At the stop look around and you will see a péage. You can hitchhike on this one if you want, but there is low traffic, so it is best to go on the big toll where all the cars from North or South have to stop. This one is 500 meters more in the south but it is completely worth to walk to it since the chances to get a lift there, greatly increases. To get there, you need to walk past the péage in the direction of traffic. It's illegal and quite dangerous to walk in the road, so you need to walk along it, but stay in the grass next to it. You will see the big péage from where it's easy to get a 300 or 400 km ride in any direction.
The "all directions" tip, above, by far seems the best bet as these two mean hitching out of a roundabout, which is never as favorable as a péage. But if in any case you need to hitch out without using the tram or péage others have used these routes:
Option One: Another option is to get to Place de L'Europe (location), for example by taking tramline 1. From there you can already see signs to the highway. You can either follow those signs and the main road (Avenue de Président Pierre Mendes France) for about 15 to 20 minutes, or get a ride from where this road starts to either your destination or to a better location further up the road, at the roundabout where the main highway A9/E15 actually connects to the Avenue de Président Pierre Mendes France.
note: there is not a very good spot for cars to stop, but they stop at the roundabout for traffic with enough time to ask drivers for a ride, and for them to open the door.
Option Two: A second option is the roundabout off Avenue de Palavas. However there is no good spot for cars to stop at the roundabout, and nowhere on the ramp either. Zac waited for an entire day for a ride to Perpignan without luck and shamefully retreated to the train station.
You can find free luggage storage at the "Musée Fabre," a big new museum in the center of Montpellier, close to "Place de la Comedie". Of course the luggage storage is for people who visit the museum, but if there is a lot of people they won't pay attention. It's a room on the left in the entrance, there are boxes where you can put a bag. You need to put one coin inside to have the key which they give you back.
It's a nice painting museum for people who like art. Use an ISIC card (or say you have one) for free entrance.