I wonder when Eliana will be old enough for this

I have seen this idea on Martha Stewart before, but thanks to our recent road trip have had renewed interest in it. I wonder when Eliana will be old enough for something like this? I'm guessing it will be sooner rather than later, I just have to put some thought and work into it. It would be nice to have some special activity bucket that's just for longer trips in the car. Currently our source of travel entertainment for her is the DVD player, and I think she could use some variety other than Blue's Clues, Veggie Tales, and the BBC Planet Earth series.