Data Stores(Saving Tools) With Loops?

There are a lot of problems with the way you are using the data store in your code, 1st you should not be creating a new data store for every player as you should be changing the key, 2nd you should not be using lighting to sore object and lastly you should not be using the on close event like this. You need to save the data when the player leaves the game not when the server closes.

Example:-

-- we get the data store at the top so we don't need to get it each time a plr is added / removed
-- The current setup tries to get a new data store for every player, you should be using one data store and changing the keys
local dsServ = game:GetService('DataStoreService'):GetDataStore('Testing')

-- Tools should be stored in ServerStorage and not in lighting
local toolList = {}

for _, tool in pairs(game:GetService('ServerStorage'):GetChildren()) do
	-- just make this into a key value pair so we dont need to loop to find each tool
	toolList[tool.Name] = tool -- tools must have different names else it will be overwritten
end

game.Players.PlayerAdded:connect(function(plr)
	
	-- we use a a key to access the player data, this key is made unique with the UserId
	local key =  'tools_' .. tostring(plr.UserId)
	
	local data  = dsServ:GetAsync(key)
	
	local backPack = plr:WaitForChild('BackPack')
	if data then
		-- data found
		for _, tool in pairs(data) do
			if toolList[tool.Name] then toolList[tool.Name]:Clone().Parent = backPack end -- add tool if found in the list
		end
	else
		-- no data found 
	end
end)

game.Players.PlayerRemoving:connect(function(plr)
	local key = 'tools_' .. tostring(plr.UserId)
	
	-- build a list of tools
	local saveList = {}
	for _, tool in pairs(plr.BakcPack:GetChildren()) do
		table.insert(saveList, tool.Name)
	end
	
	-- save tool list
	dsServ:SetAsync(key,saveList)
end)

I hoe this example helps, please comment if you do no understand how / why this code works.