The answer is the first sentence: Join Staples and me in helping students succeed.
Here is a tip for when you don't know when to use "me" or "I" in a sentence; get rid of the other subject (in this case "Staples") and see if the sentence still makes sense with the other subject (which would be "me" or "I" in this case). If it does, then you have used the correct word. If not, try the other pronoun.
Hope this helps!
