How Do I Avoid Having The Two Same Weapons?

Im Making a Airdrop Airdrop Works Well If You Dont Know The AirDrop Script, Here it is

-- Script Made By UglyPoe (RarityScript) And Minecrafter09031031 Changes The Script to Lucky Block Script
-- Instruction :
-- Make a Folder in ReplicatedStorage and Name it Tools, And then Add Weapon On It
    -- Also, Make Another Folder Name "Crates", -- This is where we put all the crate for RespawnSystem

local Weapon1 = game.ReplicatedStorage.Tools.Colorless -- Weapon 1
local Weapon2 = game.ReplicatedStorage.Tools.MagicalStaff -- Weapon 2
local Weapon3 = game.ReplicatedStorage.Tools.SaturnStaff -- Weapon 3
local Weapon4 = game.ReplicatedStorage.Tools.Determinator -- Weapon 4

local Items = {
    {Weapon1,1},
    {Weapon2,4},
    {Weapon3,5},
    {Weapon4,3} -- Higher Weight, Lower Rarity
}
local TotalWeight = 0

for _,ItemData in pairs(Items) do
    TotalWeight = TotalWeight + ItemData[2]
end

local function chooseRandomItem()
    local Chance = math.random(1,TotalWeight)
    local Counter = 0
    for _,ItemData in pairs(Items) do
        Counter = Counter + ItemData[2]
        if Chance <= Counter then
            return ItemData[1]
        end
    end
end

local click = script.Parent.ClickDetector

click.MouseClick:Connect(function(plr)
    local Tool = chooseRandomItem()
    local CloneTool = Tool:Clone()
    CloneTool.Parent = plr.Backpack

    local xyz = 1 * 60 -- Change 1 To A Number of Minute You Want

    script.Parent.Parent.Parent = game.ReplicatedStorage.Crates
    wait(xyz) 
    script.Parent.Parent.Parent = game.Workspace
end)

It works perfectly, But when i have SaturnStaff Tool, And I Click The Crate Again, Saturn Staff Appears Again, Can you Help Me Avoid Having 2 Same Tools?, Because if you Click a lot of Crates, 70 % Of player inventory is Saturn Staff , Haha

So Please Help

ADVANCED THANKS!