I would bring a little Reeses, favourite wine or liquor, maybe your favourite shampoo and soap. Any clothes others say they can't find. Play tennis so bring strings, grips and shoes.
Shaving Gel, Boots brands is just like Gillette, Cheese Makro Mainland Vintage Cheddar Cheese, Cheese Doritos in Lotus, Big C, Tops Coles Double Chocolate Brownie mix is good, Beatty Crocker Chocolate Chip cookie mix Tops, or Lotus. Shirts and shorts are cheap. Can find decent pair of shoes and add gel insoles to make comfortable. I use the Biore UV Aqua off Lazada that is value priced and it actually works well. My choice advance sunscreen good zinc oxide for pool or beach.
As others have noted with a little work you can find almost anything in Thailand.