A couple of days ago, I recommended The Natural Soap Book and The Soapmaker's Companion by Susan Miller Cavitch to a friend, as I've used home made soap (yes, it can be ugly, too) for years now. And, since I hate wasting anything, I knitted up a "soap saver," a cotton bag that is not only eco-friendly but also quite good for exfoliating while showering. The soap saver works this way: when soap gets too small to manage comfortably, just open the bag and drop it in. After a while, those small chips add up to make a nice self-sudsing scrubby. Probably the best thing about a soap saver is that it can be knitted in any size that fits comfortably in the hand and from any weight or type of yarn that is washable. I like cotton for its texture and natural fiber content.
If you want to knit your own, you don't need to be advanced--any beginner who can do garter stitch will find success! Just find the yarn you like (remember, wool and wool blends will often felt, so I'd avoid those) and use a larger needle to make a more open weave in your work. For worsted weight cotton yarn, I used a 10 or 10.5 needle; small balls of scrap yarn will do. Cast on about 25-30 stitches. Knit every row until it's the length you want. 5 to 6 inches should do it (it will stretch some when wet, due to the flexibility of the stitching). Bind off the last row loosely and fold the piece in half lengthwise. Sew up the side seam and across the bottom to make the bag.
With a crochet hook and remaining yarn, chain a length suitable for a drawstring (you'll want one long enough to thread through the open top and have enough left over to hang the loop over the shower knob). You can also make i-cord if you're experienced in that or just use a pretty ribbon that can get wet. Thread the drawstring through the top of the bag and draw it tight. Tie the drawstring together at the ends with a knot, and you're ready to save those lovely homemade soap chips!
Since I'm planning to knit up a couple more in the near future, I'll post some pictures when they're done!