The best thing to do is to have a home for your betta fish ready to go before he arrives from the pet store. You can either choose one of this setups:

• an individual small tank for one betta fish, 1/2 gallon minimum
• a glass or plastic fish bowl for one betta fish, 1/2 gallon minimum
• a divided tank for several male or female betta fish
• a community tank for one male or several female betta fish

• a live plant or plastic plant
• a net and siphon or gravel vacuum
• a pH test kit
• aquarium gravel
• most important: betta fish food
  

• a separate bucket or container for preparing water
• basic freshwater test kits especially ammonia test kits
• A tablespoon of freshwater aquarium salt
• an aquarium thermometer, and if your tank is 5 gallons or above, a heater
• water conditioners, stress relief, and medications for betta care