The island is generally pretty quiet and is a gem of coastal Cambodia. All the bungalows and restaurants for tourists are at the main beach. Besides that there are only a few fisher huts scattered around the island. Development is slow, though there is now a massage shack directly on the beach. The name Rabbit Island derives from the shape of the island, not from any rabbits there.
Koh Tonsay is a 20 minute boat trip from Kep beach for around US$8-10 return if part of a tour; alternatively, get to the boat pier before 09:00 and share a $25 boat ride (to go and come back) with others (maximum 6 people). Many people just book a day trip to the island and don't stay overnight. Beware of buying a ticket in advance for specific time through various agencies. Apparently, they do not have any scheduled services. The staff will try to arrange a boat for you, but in a way, that they are doing you a favour. Any complaints about the scheduled time will make them angry, and you'll be told to complain to your agency.
As the island is very small, you can only walk around. A hike around the island takes 2-3 hours.
There is not too much to do on Rabbit Island. It's all more about relaxing a bit off from the civilised world.
There are a few 3-4 restaurants at the main beach all serving similar dishes. Portions are big, prices cheap and the seafood is extemely fresh. Country between 4$ and 5$ for big plate of fresh cooked fish or crab.
There are a bunch of Bungalows all at the main beach where the boats arrive (US$5-10 a night). They are all very similar, the main difference being if they have a private or shared toilet and if beachfront or not. Usually they come with a mosquito net, a hammock outside and a squat toilet. Usually it is not necessary to make a reservation, just ask around for free rooms after arrival.
There is no Internet or Wifi available, however there is good reception for mobile phones with mobile internet. Electricity is only available with power generators from 6-10pm.