Hey man,
I went to Bali recently and there are a few places to check out.
Temples
The Barong & Kriss Dance at Batubulan (Bali's tradition)
Bali Bombing Memorial (Near Kuta area)
Coffee Plantation (Traditional Bali coffee)
Sanur Beach (Swimming & watersports)
Kintamani (A landmark with great view)
Kuta (Shopping)
Ubud Market (More shopping, for females)
Matahari Square (Shopping Centre)
Bali has a lot of surf wear such as Globe, Rip Curl, Billabong, Quiksilver. That's in the Kuta and Matahari Square area. I didn't manage to find guitar shops in Bali though.
Are you going with a tour?.