i can't necessarily tell you the very best things, but here is what i use
1. prime for water changes/conditioner
2.
API freshwater master
test kit, for testing, obviously

3. stress coat + occasionally if i have to repair ripped fins
4. i always keep a few different meds on hand, personally i like the jungle buddies tabs, they treat quite a few different things (
ICH, fungus, fin rot, mouth rot, parasites, bacteria, etc)
5. i also keep a bottle of tetra safe start, i haven't used it yet but i keep it as backup in case i ever need to quickly cycle a tank. as far as i know it's the only product that actually works in terms of quick-starting the cycle
6. i also have fluorite for my live plants
7. i have nitraban, but i'm questioning its effectiveness right now *shrug*
hope that helps!!!

feel free to ask more questions