Like any other filter, this one protects the front lens from water splashes. 

I have not looked for a specific travel case, but unless you are being really rough with it I would say a padded envelope or a generic small case would do it. It's pretty sturdy. I take it to to the office sometimes and just put it in one of the pockets of my laptop case. Also, for extra protection against scratches I never removed the clear plastic film that comes over the screen. Except for the red ""pull here"" tab, you can't tell it's there. 

The packaging is all matched with a hard board to ensure that the user receives the product in perfect condition 

Yes, it will fit. 

Hi, we just checked the Panasonic Leica 100-400mm lens need 77mm filter , you can reconfirm your lens mark as "Φ" (diameter) , thanks.