Cola tool not doing what script says to do (Slurp, +1 leaderstat point) ?

Don't name your functions and your variables the same thing. Rename your slurp function to something else. Also, you have to use the assignment operator to add to a value. This is also not a good idea because you're getting LocalPlayer from the script, so I'm assuming you're using a LocalScript. Playing animations or changing value on the client (LocalScript) does not replicate over to the Server, so only the player using the cola will see the effect, or hear it, or even the addition to their leaderstat. If you want the whole server to see it, I'd recommend using a ServerScript. You're also trying to play the audio from StarterPack, not in the actual tool itself.

Fixed LocalScript:

local tool = script.Parent
local slurp = tool.Slurp -- see below as to why i changed this
local Lplayer  = game.Players:GetPlayerFromCharacter(tool.Parent) or tool.Parent.Parent;
-- this is because ServerScripts don't have access to LocalPlayer, so we get it using their character OR if it's in their backpack, we go up twice
local leaderstat = Lplayer.Leaderstats
print(leaderstat)

  function playSlurp()
   slurp:Play()
   wait(0.5)
   print("Slurping")
end

  local function onActivate()
   playSlurp()
   wait(0.1)
   print("Adding")
   leaderstat.Points.Value = leaderstats.Points.Value + 1 -- adding to it's current value
   print("Added")
end

tool.Activated:Connect(onActivate)

Fixed ServerScript:

local tool = script.Parent
local slurp = tool.Slurp -- Changed this so that it gets the audio IN the tool and can play it
local Lplayer  = game.Players.LocalPlayer
local leaderstat = Lplayer.Leaderstats
print(leaderstat)

  function playSlurp()
   slurp:Play()
   wait(0.5)
   print("Slurping")
end

  local function onActivate()
   playSlurp()
   wait(0.1)
   print("Adding")
   leaderstat.Points.Value = leaderstats.Points.Value + 1 -- need the value, not the object
   print("Added")
end

tool.Activated:Connect(onActivate)