Episode 1: Hikki gets a homemade cookie from Yui for his help. Despite the cookie's dubious taste, he still eats it as an acknowledge for gratitude.
Episode 6: Yukino going extra mile to congratulate Yui with her birthday, and solving the club members' differences in the process.
Both Yui and Hachiman pay a visit to a sick Yukino and, basically, say that if she doesn't want to rely on strangers, she can rely on them instead.
Yukino: "Well, it might be hard for me now, but one day I'll definitely rely on you. So, thank you."
Yukino's timid parting wave to Hachiman. Besides being really adorable, it shows how much she opened up to people in general and to Hachiman in particular.
Episode 12: One of the few moments where Hiratsuka isn't abusing Hachiman. After he ruins his reputation by verbally tearing into Sagami, she reminds him that his twisted attempts to help others shouldn't mean that he should always sacrifice himself.
Episode 13: "Good job there", "The rest is up to you", "Hikki, do you best" and a casual high-five. All service club's trust and friendship in three phrases and two gestures.