try to index nil with FindFirstChild Help What do I do? It is a SaveTools

    local Backpack = Player:WaitForChild("Backpack")
local StarterGear = Player:WaitForChild("StarterGear")

if ToolData ~= nil then
	for i, v in pairs(ToolData) do
		if ToolFolder:FindFirstChild(v) and Backpack:FindFirstChild(v) == nil and StarterGear:FindFirstChild(v) == nil then
			ToolFolder[v]:Clone().Parent = Backpack
			ToolFolder[v]:Clone().Parent = StarterGear
		end
	end
end

Player.CharacterRemoving:Connect(function(Character)
	Character:WaitForChild("Humanoid"):UnequipTools()
end)

Some parts of the script I deleted it because it was not shown so I deleted some parts I am showing in the part where the error is

On line 6

FindFirstChild will return true or false when used in an if statement saying if it exists or not checking if it is nil will return an error and you should check if it is not StarterGear:FindFirstChild(v) or if StarterGear:FindFirstChild(v) == false I fixed your code below.

    local Backpack = Player:WaitForChild("Backpack")
local StarterGear = Player:WaitForChild("StarterGear")

if ToolData ~= nil then
    for i, v in pairs(ToolData) do
        if ToolFolder:FindFirstChild(v) and not Backpack:FindFirstChild(v) and not StarterGear:FindFirstChild(v) then -- Checking if FindFirstChild(v) is nil can not be checked as it returns a bool value.
            ToolFolder[v]:Clone().Parent = Backpack
            ToolFolder[v]:Clone().Parent = StarterGear
        end
    end
end

Player.CharacterRemoving:Connect(function(Character)
    Character:WaitForChild("Humanoid"):UnequipTools()
end)