Plot hole: Both Vesper and James are needed alive if Le Chiffre is to steal the money. But the trap on the road could have easily killed at least one of them (Bond isn't looking too good afterwards), or even both.
Plot hole: During the last half of the movie, it's a matter of discussion if it was Vesper or Mathis who informed on Le Chiffre about his "tell" (give-away when he was bluffing). But it could just as easily have been a trick that the latter had planned all along - it didn't have to be either of the other two. After all, we're talking world-class poker players; why would it ever have been that easy to see through Le Chiffre's game?
Answer: From the novel: "Three measures of Gordon's, one of vodka, half a measure of Kina Lillet. Shake it very well until it's ice-cold, then add a large thin slice of lemon peel."
Captain Defenestrator