Help with DataStores?

Data Stores cannot save instances themselves (A tool is an instance) So, to save a player's backpack I put tools in the "ServerStorage" like so: http://gyazo.com/3746b89ded1f686afb71ad8c97a935dc

local ds = game:GetService("DataStoreService"):GetDataStore("tools")
local defaultTools = {game.ServerStorage.Pistol,game.ServerStorage.Sword} --The values in this are instances of tools. That can be cloned.
game.Players.PlayerAdded:connect(function(ply)
	local key = "user_"..ply.userId
	local playerTools = ds:GetAsync(key)
	if playerTools == nil then --If the value is nil then use the default tools
		for i,t in ipairs(defaultTools) do
			local newClone = t:Clone() --Because the values in the defaultTools are instances they can be cloned
			newClone.Parent = ply.Backpack
		end
	else
		for i,pt in ipairs(playerTools) do --Loop through the tool names
			for i2,st in ipairs(game.ServerStorage:GetChildren()) do --Loop through the tools in ServerStorage
				if st.Name == pt then --If the tool name is equal to the saved string value
					local newClone = st:Clone()
					newClone.Parent = ply.Backpack
					break --No point looping through the rest of the children if it's already been found, breaks out of the "GetChildren" loop.
				end
			end
		end
	end
end)
game.Players.PlayerRemoving:connect(function(ply)
	local key = "user_"..ply.userId
	local playerTools = {}
	for i,b in ipairs(ply.Backpack:GetChildren()) do
		table.insert(playerTools,b.Name) --Inserting the tool's name
	end
	ds:UpdateAsync(key,function(old)
		return playerTools --Saves a table of the names of the tools that are in the player's backpack
	end)
end)

When the player joins the game (when the "PlayerAdded" event is called) then the "GetAsync" is called to retrieve the player's saved backpack. If they haven't saved then the value will be nil. So, I created a table (defaultTools) that stores the Instances of Tools in the ServerStorage. This is looped through and adds to the player's backpack. However, if the retrieved backpack is not nil then the stored values are names of tools. This is looped through, then looping through the children in ServerStorage and checking if the values are the same then if so, adding a clone of the Tool instance (in ServerStorage) to the player's backpack.

Then, when the player leaves ("PlayerRemoving") I looped through the player's backpack adding the tool's name to a table which is then saved using "UpdateAsync".

Hope this helps. I have tested and it works for myself.