private final Map<String, ArrayList<ItemStack>> items = new HashMap<>();
private final Map<String, Inventory> inventories = new HashMap<>();

private final Inventory inventory;


public YourClass(){
   initItems(); // Add your kits to items.
   for (String kit : getConfig().getConfigurationSection("Kits").getKeys(false)) {
      inventories.put(kit, Bukkit.createInventory(null, findACorrectSize(items.get(kit).getSize());
   }

private final int findACorrectSize(int size){
  if (size < 9) return 9;
  else if (size < 18) return 18;
  else if (size < 27) return 27;
  else if (size < 36) return 36;
  else if (size < 45) return 45;
  else if (size < 54) return 54;
  else return 54;
}

}