We stayed in the southeastern area of Samui so my tips are geared more to that area. Since we rented a house we didn't dine out for every meal but did eat dinner out every night, and most lunches. Breakfast was at home.
La Fabrique - Lamai and Chaweng
This is a very good French bakery and cafe where we bought our bread. The rye is good but the whole grain is fantastic. Makes wonderful toast. We always went to the Lamai location which is only a couple of doors away from Wat Lamai and very near the Tesco Lotus Lamai. It's always busy and the food is great.
Shopping on Samui
There are many Tesco Lotus (super) stores and Tesco Express shops. We did all of our shopping at Tesco Lotus Lamai - food, household, sandals, DVD's, just about anything. Most items are labeled in English and Thai but a few are Thai only and you have to rely on the photo. There are many European and American brands. In the Tesco mall where we shopped there was a Dairy Queen, KFC, Dunkin Donuts, etc (none of which we stopped at). And there are McDonalds as well - which we did not eat at either.
Krao Chao Baan
This restaurant was walking distance from our house and we ate here at least twice a week. This is my Tripadvisor review.
Another restaurant where we ate at least twice a week.
A restaurant and location we LOVED.
Also visited this one many times:
Lai Thai Taling Ngam is in the south of Samui. There is a restaurant with the same name in Mae Nam which is in the north. I have submitted a new listing to Tripadvisor for this restaurant but it hasn't yet been published. A Google search 'Lai Thai Taling Ngam' will get a map and directions.
The food, location overlooking the sea, the staff - all fabulous!
Black Canyon Coffee
Best coffee of every conceivable kind, hot or cold: We always went to the one in Tesco Lotus in Lamai.
Mobile phone sim card and data package: Since we had time we got our sim and data package in Bangkok Airport arrivals hall at DTAC. I bought 30 day packages and to top up or change the package I went to the DTAC shop in a shopping mall called Big C which is just a short distance down the road from Tesco Lotus Chaweng.
We hired a car at a monthly rate from our accommodation (they own a few cars and motorbikes which they rent out). There are many places to hire cars on the island, but check on the deductible on the insurance.
Driving a car on Samui, once you get used to be surrounded by motorbikes which pull in front of you, makes the stay very convenient. Parking can be a bit difficult as motorbikes receive priority parking in many places. Motorbikes can be rented very cheaply but you are expected to drive most of the time on the hard shoulder which you share with bicycles and pedestrians. We saw many people bandaged and scraped and hobbling on canes which we attributed to motorbike accidents. Almost all looked like tourists.
We still have not visited every single temple (Wat) on the island but will see the rest when we return.
Temples and other sightseeing tours
We wanted to take this trip: Blue Star kayak trip to Angthong Marine Park. But either the weather didn't cooperate, or we had visitors who didn't like the idea of kayaking.
So an alternate plan was a long tail boat trip with: TK Tours
Four of us chartered a boat so that we wouldn't need to go with a group. We snorkeled and went swimming for 2 1/2 hours.