So after years of periodically making guitar art, I actually went out and bought a guitar. So it's time to make accessories...
First off, here's a bulky yarn/padded, two color strap cover:

I bought a pink strap because it's so obnoxious that I'll want to make covers for it :) Should you feel like making one, I cast on 10 stitches with size 11 needles and knit until I ran out of yarn--it's a good way to use up spares. Note that when you sew the sides together, don't do it "right sides together" (not that there are any) and then flip it inside out-- the strap lays flatter if you don't flip.
Next up, I'm working on a fair isle pattern with little electric guitars going up the strap. And I'm in process of designing an electric guitar sweater.
And in my continuing quest to figure out what to do with guitar picks, I've designed my own little guitar pick pouch. It has a buttonhole on one side and the loop goes in through it to keep it shut. You can use it as a keychain, pin it to a strap, or make a longer chain for jewelry wearing. It holds more than other holders I've seen--crammed 17 picks into one so far :)

Uses worsted weight yarn and size 5 DPN's.
- Cast on 4 sts. Put 2 sts on each needle. You'll go back and forth between knitting on each needle so that it's "in the round"-ish--but flat. So when you do one side, do the same thing on the other until you're ready to close the bag.
- On each side, kf&b both sts--should have 4 sts on each needle.
- On the first and last stitch in each row, kf&b, k stitches in the middle. Repeat doing this until both sides have 8 stitches on the needle.
- Knit each side for 6 rows.
- On each side, k2tog, knit to last 2 sts, ssk. Should have 6 sts left.
- Knit, k2tog, ssk, knit. Should have 4 sts left.
- On one side only (front), knit 1 stitch, bind off 2 sts--should have 2 sts with a break in the middle, buttonhole-style.
- On the next row, knit, cast on 2 sts, knit.
- Bind off all stitches. Reconnect your yarn on the other side.
- On the second side, knit 2 stitches. Leave the other two stitches on the needle/a holder--we'll get back to them later.
- On working needle, knit in stockinette for 7 rows (or do i-cord, if you prefer), or for as long as you'd like to make the chain.
- Cut yarn, leave stitches on needle and go back to working on the second side of stitches. Do the same thing until both sides are even.
- Put all 4 sts on needle, bring yarn in the middle to the start of the row. Knit across all 4 stitches, then bind off on the next row.
Slip cord through buttonhole to hold pouch closed.
I also tried doing a crocheted band to make the bracelet version. I drew a crochet hook through one of the two stitches on the side and used it to bind off the extra stitch, then made a chain and connected it to the other two stitches ("binding one off" again). I then did a row of single crochet along the band to strengthen it.