Dave,
A line stripper is used to remove old line off of your reels. I use a model made by Rapala, its battery operated and is very simple and fast to use. Of course you could just release the bail and remove it by hand but after 3 or 4 reels it can get old quick. I change line on all my rods quite often and carry about 20 different setups on board, so it comes in handy for me. Mine also has a hook sharpener built onto the end of it, so whatever bait i tie back on to the rod i can give the hook a quick tuneup too. Its basically all personal preference but i think its a good tool to have. Shouldnt cost more than $15 or so..
See ya on the water,
Mike