How necessary is it to make reservations for lunch in Paris if I am planning to eat in relatively casual bistros (no starred restaurants)? I know that reservations are always preferred, but I wanted to leave some spontaneity to my January trip. Is it inappropriate to just walk into a bistro for lunch and ask to be seated (2 people)? I have some restaurants in mind, but I am afraid that reservations during the day would be a little restricting. I would appreciate any advice. Thanks!