Why does this backpack script not work?

First you'll need to put it in a server script in the workspace or what ever you want but not in the player.

We'll make it a little more clean before and fix your error, I mean put the ends where you forgot to put it.

Second, we'll add theses events for make your Game_Tools more cleaner and we'll do for when the player leave the folder get destroy, without that you can get so many folder when the player left and It can make it glitch.

After, we'll create the main function and put the body in.

Finally, we run the function with a loop for while 60 secondes your function will run.

--local tools = {"AK14", "Pistol", "Shotgun"}--I don't know what you want to do with that so I comment it.
local newParent = game.Lighting["Game_Tools"]

game.Players.PlayerAdded:connect(function(player)
    local playerSlot = Instance.new("Folder", newParent)
    playerSlot.Name = player.Name
end)

game.Players.PlayerRemoving:connect(function(player)
    local playerSlot = newParent:FindFirstChild(player.Name)
    if playerSlot then
        playerSlot:remove()
    end
end)

function main()
    for _, player in pairs(game.Players:GetPlayers()) do
        local backpack = player:WaitForChild("Backpack")
        for _, tool in pairs(backpack:GetChildren()) do
            if tool:IsA("Tool") or tool:IsA("HopperBin") then
                tool.Parent = newParent
            end
        end
    end

    wait(10)

    for _, playerSlot in pairs(newParent:GetChildren()) do
        local player = game.Players:FindFirstChild(playerSlot.Name)
        if player then
            local backpack = player:WaitForChild("Backpack")
            for _, tool in pairs(playerSlot:GetChildren()) do
                tool.Parent = backpack
            end
        end
    end
end

while true do
    wait(60) --Wait 60 secondes before run the function
    main()
end

enjoy !