For new arrivals: paying for things in France is easy by credit card, but as a resident you'll soon need a French bank account. Here are the basics on how to set up and manage your French account. The official French currency is the Euro.
If you need a prescription refilled immediately or are looking for over-the-counter medication to alleviate a flu or headache, forget about finding a corner drugstore in Paris - they don't exist. Look for a flashing green cross instead. In France, only pharmacies are permitted to sell most over-the-counter medications, and pharmacies are rarely found at supermarkets, contrary to North America. Use this directory to Paris pharmacies open late or 24 hours a day to find a location close to where you're staying.
France has just one public postal service, called La Poste, this entirely state-run organization is generally efficient, although occasionally subject to strikes. There are post offices, called bureaux de poste, in every urban neighborhood and most rural villages, and are easily identified by their blue and yellow logo.