How does one insert Backpack items into a string?

To insert something into a string, I'm assuming that you are looking for a method of storing the names of the tools a player had into a string so they can load them up again.

I like to use Data Persistence because the ROBLOX wiki has a fairly poor explanation of how DataStores work.

You would do this like so: (Not tested)

game.Players.PlayerRemoving:connect(function(player) -- When a player leaves the game
tools = player.Backpack:GetChildren()
for i = 1, #tools do -- Getting all the tools in their backpack
player:SaveString("Tool"..i, v.Name) -- Saving the name of the tool
for i,v in pairs(player.Character:GetChildren()) do
if v:IsA("Tool") then -- Getting tool in character if there is one
player:SaveString("Tool"..i+1,v.Name)  -- Saving the name of the tool
end
end
end
end)