I made my Booga Bag 3 years ago. It was my first felting experience, and I made it by hand... NEVER again by hand! Too painful... 
Anyway. I have never used my Booga Bag because I wanted to line it before, to protect it from keys and other sharp items that could damage it, but I was not sure how to do it...
Taking my sewing machine out yesterday, has motivated me I guess, because I DID IT!!! I used leftovers from the Toddler Dress. A 100% cotton fabric that I bought when I was pregnant with my son, to make sheets for his crib (I never did... 
)
Now, my liner is not Quilted-like-accuratly-made, as I was totally impovising as I was going, but I think it is about right. I even have added a little inside pocket as well...
[Click on photos to enlarge]
I neither took notes nor measurements of what I did, so I am not sure I would ever able to do the exact same thing again if I had too... but one thing for sure, I am not afraid of lining bags anymore! 
