Since Napili Shores and Kapalua are kind of like the "last little areas" west of Maui Napili General store is a small store back in our little corner of the world. You CAN drive about 1 mile up the road to the Napili Shopping Center but if you just want to stop in and by some postcards, a can of soda, or a hiking book on Maui you can do these things at the Napili General store with a 30 second drive from Napili Shores Resort or if you feel like getting out for a walk, you can walk to the store.
What to buy: I bought postcards and a "Maui Revealed" book (things and hikes to do in Maui).
What to pay: This store is a bit more expensive than normal for some items. Postcards were priced reasonable and the books like "Hike Maui" and "Maui Revealed" were priced at their regular retail prices. However, things like t-shirts and lotions were expensive at least compared with the stores in Lahaina .
Close to Napili Shores Condos and Kapalua Resort. If you just want to rent some snorkel gear for a day you can get good gear for about $5 per person per day. Cheaper rates apply if you rent the gear for an entire week, I think it ran around $10 for a week.
What to pay: $5 per day for snorkeling gear or around $10 per week per person. You will need to check the current rates when you go though, they may change.