Ally punching out the off-duty cop for harassing Jack. Doubles as a Moment of Awesome as they're in a bar full of cops when this happens. Moreso because this is right after Jack confides in her about how much it bothers him that people stop treating celebrities like real people after they get famous
After the aforementioned punching incident, Jack's fumbling attempt to treat Ally's bruised and bleeding knuckles. Notable in that the typical Hard-Drinking Rocker Archetype that Jack is meant to represent would be elated to find a rough-and-tumble "Cool Chick" who's not afraid to throw a punch and start a barfight. But what does Jack do? Carry Ally out of the bar and immediately take her to the store to get ice packs (well, frozen veggies; he's doing his best) and bandages. Awww...
Related to the above, when the checkout clerk sneaks a photo op with Jack, then immediately apologizes. Jack tells her it's fine, but Ally, knowing how Jack actually feels about that, bluntly tells the woman it's not.
Ally finding out she's been nominated for three Grammys. Special shoutout to the way Gaga acts the scene, you feel every ounce of Ally's disbelief, amazement, excitement, fear, and whatever else an artist might feel after having worked so hard for their art only to finally achieve the ultimate sign that they'd made it.
Just how encouraging Jack is of Ally and her music. Again, you would expect a character like the one he represents to grow jealous of Ally and her rise to fame especially as his star fades, but Jack is always ready to give Ally the spotlight. The only time he ever lashes out at her is when he feels she's not being true to herself artistically—and even then, he apologizes right after and accepts that he was wrong. Jack’s supportiveness is what makes his suicide even more heartbreaking.
When he asks Ally to go to Memphis with him for moral support through an unpleasant gig at an AARP concert, Ally can't go because she has to work on her album. She starts to apologize but Jack cuts her off:
Jack: Listen to what you're saying. Listen to what you just said. People want to hear what you have to say. That's the stuff right there. Take it in.
Jack thanking Ally with the following lines, especially because at the beginning of the film when his driver talked about his family, Jackson sullenly remarked that he doesn't want to go home and asked his driver to take him to a bar instead. The contrast between these lines and the earlier moment just shows how deeply alone and miserable Jack was prior to Ally coming into his life. To say she became his muse is an oversimplification, she became his family.
Jack: Thank you, by the way.
Ally: For what?
Jack: Giving me a home. This place never felt like home, 'til you came.
Jack's proposal and his and Ally's subsequent impromptu wedding; d'awww.
The video from the drag queens congratulating Ally on her success and telling her to come back soon.
