I know they're supposed to be eaten the day purchased, but we can't finish one in one day around here...and it's inconvenient to get to the local store where sold. They're pretty decent ones from a Brooklyn bakery.
I've saved the long paper bags and find that if I wrap the leftover portion in two or three bags, it's pretty edible the next day. If wrapped in plastic bags or Saran Wrap, the crust goes soft.
Of course, toasting or heating often helps too, but that's not ideal.
How do you deal with leftover baguettes?