There are two basic Thai restaurants and limited convenience shops on Ko Surin, all run by the national park.
Like Thailand's other national park islands, Ko Surin features two open air restaurants, one at Kong Khad and another at Mai Ngam. Each are spacious and feature long communal tables that make for good chatting with other travellers. The menu is mostly basic Thai food between 80B and 200B. Basic western breakfasts and sandwiches are also on offer along with coffee (Nescafe), tea (Lipton), and Chang or Singha beer along with the usual sodas and bottled water.
The restaurants are open from 8:00 to 13:00 and again from 17:00 to 20:00. They shut down completely at 20:00 so be sure to grab a couple extra beers before then if looking to stay up socialising until lights go out at 10:00.
A small shop is also open at each location from 8:00 to 20:00, and these sell basic toiletries along with bottled water, Mama cup noodle soup, and a few chips and cookies.
If staying on Ko Surin for a few nights it's advisable to bring along some fruit and/or snacks from the mainland.