This French Wikipedia article quotes a crackpot scholar as saying that around 1,200 Celtic words are known, of which French has 200; it gives these examples: bief, if, bille, soc, ruche, claie, barque, chemin, lieue, lande, grève, roche, char, bec, jarret, briser, changer, border, petit, dru. I have no idea how many of those are trustworthy. A 1991 source gives 147 Celtic words, but doesn’t distinguish inherited words from borrowings (it includes backgammon, for instance).
French char ‘a tank’ is indeed of Celtic origin. French inherited it from Latin carrus, which has also led, via Old French or Old North French, to English carry, carriage, chariot, and charge. Spanish has also given English the doublet cargo.