Prime by Seachem water conditioner, only silk plants do not buy plastic ones, gravel and i like bigger stone it easier to do water changes, best heaters are
Penn Plax Cascade
Hagen Elite Mini Submersible
Most of, if not all of these heaters have to be ordered online or found in a local fish shop. Petsmart and Petco generally don't carry them. Good places to order are www.amazon.com
How big is your tank?
When you go buy first time make sure he/she doesn't have any sing of the disease. A lot of time you can get sick betta.
When you bring betta home i would suggest quarantine it in emty tank before you put gravel in or plants in case it will sick.
I would suggest water conditioner Prime because it the best in case you have problem with your tap water- it most recommended water conditioner
Food : New Life SPECTRUM Betta Formula, Aqueon BettaFood, you can buy freeze dried blood worms which you can feed only as a snack 2 times a week . If you will buy blood worms make sure you don't feed him untill he will learn how to eat pellets. Pellets are better than flakes or blood worms but if you will offer blood worms they can refuse pellets then.
Buy aquarium salt at the pet store and Epsom salt at any pharmacy department as first aid .
Also when you bring betta home you need to acclimate him to the new water . Make sure new water temperature is approximately the same as his. I do it this way i have my betta in the changing cup with about 15 % of the water and i am adding new water about every 5 min for about 5 times. Always cover container to prevent him jumping out, as bettas knows as good jumpers. Also leave space between water level and top of the tank.
Give us update on your new betta :)
Hadoken Kitty sorry i did't see your post as i am at work and takes me long time to write:)