When I was in the hospital a few years ago I had to have a PICC line put in. Now it definitely wasn't the most pleasant experience in the world, but it sure did beat getting poked repeatedly in the same spot. To cover the tubing coming out of my arm, they gave me a flimsy gauze sleeve which functionally did the job, but did nothing to hide it. Now that's all well and good in the hospital, but I still had my PICC line when I went back to work, and people commented on it constantly. Anyone that's been in a similar situation knows how annoying that is. Well today on ravelry I found this great pattern for a PICC line cover. Just a simple knitted tube, but holy cow would that have been nice to have! This is a great way to use that leftover yarn, I'm definitely going to start making these. They would also be cute with stripes or cables to make them a little fancier.
Here is a website with some more information about these http://findingjennproject.blogspot.com/2009/02/original-picc-cover.html
It does look like the website is a couple years old with no recent updates, so if you're planning on doing these you might want to check with a hospital about donations. For CF specifically you can visit http://www.cff.org/ to find a CF center near you.