Champagne, Burgundy, Bordeaux, Rhone, the Loire Valley... France is the home of wine.
Beer lager is also extremely popular, in particular in northern France, where "Biere de Garde" can be found.
The alcohol purchase age was recently raised to 18 for all drinks, but this is not always strictly enforced; however, laws against drunk driving are strictly enforced, with stiff penalties.
Wine and liquors may be purchased from supermarkets, or from specialized stores such as the Nicolas chain. Nicolas offers good advice on what to buy specify the kind of wine and the price range you desire. In general, only French wines are available unless a foreign wine is a "speciality" with no equivalent in France such as port, and they are classified by region of origin, not by grape.
Prices of food and beverages will vary according to whether they're served to you at the bar or sitting at a table - the same cup of espresso might cost €0.50 more if served at a table than at the bar, and €0.50 more again if served out on the terrace. Really, you're not paying so much for the beverage as for the table spot. Do consider the bar, though - while you will have to stand, café bars are often where a great deal of public discourse and interaction happens. In any event, cafés are required by law to post their prices somewhere in the establishment, usually either in the window or on the wall by the bar. Note also that cafés in touristy areas, especially in Paris, tend to serve very expensive food of rather average quality. Unless you are dying of hunger or thirst, avoid the places that have menus in multiple languages or are near heavily-trafficked attractions. Instead, consider buying snacks and beverages from a grocery store and enjoying them in a nearby park.
There are a couple of mixed drinks which seem to be more or less unique to France, and nearby francophone countries.
Is an anise-based licorice-flavoured spirit, similar in taste to sambuca or ouzo, that is served with a few lumps of sugar and a small pitcher of cold water to dilute the liquor. it is traditionally enjoyed on very hot days, and as such is more popular in the south of the country but available more or less everywhere.