What are you dispensing? That has a lot to do with what documents are needed. It is one thing to dispense a night splint or cam walker, it is another thing to dispense diabetic shoes/inserts.
For example, to dispense a cam walker, the treatment note needs to state that the patient requires one due to medical necessity, why/what they need one for, how the cam walker will help the patient, and that one was dispensed with full instructions on use, and that the patient was fitted for said walker, and it appears to be of a good size, fit, etc. as well as stating some information about the item itself... "A size large Darco BK cam walker was dispensed". So the treatment note is in essence the 3 documents you mentioned all in 1. Additionally, you need to have the patient sign a proof of delivery form with a description of the cam walker(make, model, size), and also provide a copy of your office's DME warranty policy for the item to the patient, and document that. If an ABN is applicable to the patient for some reason, you need that completed and in their chart. Of almost anything, the proof of delivery form can be the most important at times. That is what you need to prove the patient actually got the item, if ever audited.
Now, if we are talking about something like diabetic shoes/inserts, you basically need a whole tree worth of paper when it comes to documents. So it really depends on what you are dispensing, like I said.