how do I get tools to save after you leave or die?

(I may be wrong I'm new to scripting) You would need a value to assign a person a tool and after you have that value you can just datastore, for example:

--//DataStore (I'm too lazy to do it but here take this :p)
game.Players.PlayerAddded:Connect(function(plr)
    local stats = Instance.new("Folder", plr)
    stats.Name = "Stats"

    local knife = Instance.new("StringValue", stats)
    knife.Name = "Knife"
    knife.Value = "N/A"
    --//DataStorage Goes Here
end
--//Check Tool
game.Players.PlayerAdded:Connect(function(plr)
    if player.Stats.Tool.Value == "BoxKnife" then
        local boxknife = game.ServerStorage.Tools.BoxKnife
        boxknife.Parent = game.StarterPack
    end
end
--//GiveTool(Lets say you buy them by pressing a button)
script.Parent.MouseButton1Click:Connect(function(plr)
    script.Parent.Text = "BOUGHT"
    plr.Stats.Knife.Value = "BoxKnife"
end

Something Like This (I thought of that in half a minute)