The best test kit (accuracy) is Salifert, but they do not make a complete kit. As for complete kit, the easiest to use, while still being accurate, is Aquarium Pharmaceutical.
Chemicals that are always good to have on hand:
-pH buffer (SeaChem's 8.2 is generally pretty good)
-some sort of biological bacteria (NitroVec, Stability - in case there is an emergency ammonia spike and you do not have water for a quick water change)
-Iodine (Lugol's or Tropic Marin - so that you can do a quick coral dip if something looks bad or has a bad bug on it)
Cannot think of any more. More people will have suggestions, I am sure.