Make sure when you pick your train after seeing Giverny that you research ahead of time and pick a fast nonstop train back to Paris. I did this but then missed it. Should have waited two hours for the next good train. Instead we got on a slow hot train that stopped what seemed like twenty times! It was sweltering hot and crowded. Learned a big lesson.
Giverny was wonderful, especially with tickets I bought ahead of time! There was a long, long line for people without tickets. Watch for special entrance for people with tickets. I think it was gate G. Afterwards we ate at a cafe where you went through a line to get your food and could get a nice cute table outside in the shade.