Scotty's music in Kalaheo is a great shop, nice folks and very reasonable prices. I got a great deal on my Pono there.
As far as food goes, +1 on the frozen Mai Tai at Keoki's, can't go wrong with those.
My favorite food on Kauai is hands down Mark's Place, in the Puhi Industrial complex. http://www.marksplacekauai.com/ Just get anything, it will be awesome. Do NOT let the look of the place fool you, food is served in styrofoam plate lunch containers, but it is amazing. Really. Be sure to check the specials, often surprising stuff that is way beyond typical plate lunch fare. They only have picnic tables outside to eat on, this is not fine dining We would usually just take it back to our place.
Also, you must get some malasadas from the little stand out in front of KMart at Kukui Grove center. Go in the morning, she only makes them until she runs out of dough.
Hope you get to see Aldrine play!
Pueo knows his stuff!
I would add Seafood Express in Lihui to your list of places to eat as well as Hamura Saimin. Those malasadas are a MUST!