Thong Nai Pan (or just TNP among backpackers) is an area on the northeastern tip of Ko Pha Ngan that includes the two beach resorts of Ao Thong Nai Pan Noi and Ao Thong Nai Pan Yai. They are maybe the most secluded yet developed beaches on the island.
Yai means "large", and it's the larger and more developed of the two beaches. Noi means "small", and the beach here is about half the size of Yai. Noi is just north of Yai. The two are a 15-minute hike apart.
From the island's harbour at Thong Sala, there will be one or more songthaews waiting, holding up signs with their destinations. Price is a fixed 300 baht/person. Some taxis don't go to both beaches, so check for the Noi/Yai extension on their signs. As the beaches are less travelled and a long ride, sometimes you'll have to wait for the next boat to arrive, or even the boat after that, because the driver won't drive up and down for just 1 or 2 passengers. Once begun, the trip is about half an hour.
Since you've chosen this destination you're unlikely to be in a hurry. But if, for some reason you are and you are a little bit more adventurous, then catch a quick ride to the town (or even walk. From the harbour, take a left on the main street till the roundabout). Here you can rent a typical Thai 125 cc motorbike (~200 baht/day) or a 4 x 4 for 700-1,000 baht/day. It's about 15 km and it will take you around 30-40 minutes to drive.
The road to Thong Nai Pan begins at Ban Tai village (on the main road between Thong Sala and Haad Rin). The road from Ban Tai to Thong Nai Pan is 13.4 km and about half of it is now paved. From the first mountain outside of Ban Tai to the Than Sadet turn off, the road is unpaved all the way and has some nasty hills with lots of dust and gravel. Once you get to the Than Sadet turn off, the road is concrete the rest of the way (7.5 km) and much better. Care should still be taken as there are some deceptively sharp dusty corners. The improved road from the Than Sadet turn off to Thong Nai Pan has greatly reduced travelling times.
There is really not much to buy here. There are, however, 3 ATMs within spitting distance of each other in the financial district of Thong Nai Pan Noi. Also in Thong Nai Pan Noi you'll find a pharmacy which also sells second-hand books. Don't expect much of it, but when you have decided to stay one extra week in this little paradise, it might come in handy.
Fresh, deliciously steamed or grilled fish. Available at a few places, usually advertising the fish by having them on display on ice in front of the restaurant.
All places in town are very much alike, i.e., open bamboo construction with cold beer in the fridge, Western music on the stereo, and a very relaxed atmosphere. Also on the beach you can find a couple of these bars. Some of them, being part of a guest house, close between 22:00 and 23:00. Others stay open till around 02:00.
There are villa rentals in the area with private pools as well as guest houses of different ranges all along the beach plus a couple of hidden places in the village. Prices for a bungalow at the beach range, depending on the season, from 200 to 1,200 baht. So drop your bags at one of the bars and start picking out the ones you like best. At both ends of the Ao Thong Nai Pan Noi there are some classy resorts in the splurge range. Accommodation is cheaper on Yai Beach.
The village rooms will give you a more local experience so don't be afraid to go back from the beach a bit.
There are several Internet cafés charging steep prices for Thai standards of 3 baht/minute. There is also Wi-Fi available on both beaches (Ban Pong on Noi Beach, Indian Bar on Yai Beach) for around 150 baht per hour, so bring your laptop.