How to give certain player certain hats when they spawn?

Your Problem can be solved using Humanoid:AddAccessory() function. First off, Get the Accessories/Hats you want Create a Folder inside [ServerStorage] now Put the Accessories in the Folder Insert a Script into [ServerScriptService] Write this Code:

local Players = game:GetService("Players")
local HatsFolder = game:GetService("ServerStorage"):WaitForChild('FOLDERNAME') -- i'm pretty sure you can fix this for your own.
local VIP = {'ROBLOX','BuilderMan','Shedletsky'} --Replace The Strings with the players who will get the Hats, you can Add multiple Players to this Table

Players.PlayerAdded:Connect(function(p) -- 'p' is the player who just joined
    for i,v in pairs(VIP) do
        if p.Name == v then
            p.CharacterAdded:Connect(function(char) --Fires when the Character Spawns/Respawns
                wait(1)
                local Humanoid = char:WaitForChild('Humanoid')
                for _,hat in pairs(HatsFolder:GetChildren()) do wait() --yeah.
                    if hat:IsA('Accessory') or hat:IsA('Accoutrement') or hat:IsA('Hat') then --Checks if the Instance is a Hat/Accessory
                        local hat_clone = hat:Clone()
                        Humanoid:RemoveAccessories() --Comment/Remove this line if you don't want the Player's Avatar Hats to be Removed
                        Humanoid:AddAccessory(hat_clone) --Finally adds the Hat.
                    end
                end
            end)
        end
    end
end)

Note: You'll need to Edit some lines to make it work, don't Copy and Paste the Code! Instead of that, Study it and try to understand how it works!