Memories that conjure patronuses:
Ron:
Seeing Hermione wake up after being petrified
Harry telling him that the Burrow was the best house he'd ever been inHarry saying that Dumbledore knew he'd want to come backRon tearfully telling the twins what he thinks Harry is going through at Privet Drive and instead of making fun of him, Fred wipes his tears while George says "we'll just have to go get him then, won't we?"
Hermione:
Being rescued by Harry and Ron from the giant troll
Getting accepted to HogwartsAdopting CrookshanksRon squeezing her hand when they see Harry is alive
Ginny:
Realizing Harry wasn't killed by VoldemortLuna befriending her in their second year while others have avoided her because of Riddle's influence last yearWinning the big quidditch game and getting kissed by Harry for the first time, all in the same day no lessSeeing Ron be impressed by her as she practices curses
Luna:
Dancing around with her mother as a little kid while her father smiled and workedThe first time Harry complimented her spellwork in a DA meeting
Going to a Wizard Rock concert with Ginny one summer night, her first summer adventure with a friendGinny asking her and Neville to reform the DA while Harry, Ron, and Hermione look for horcruxes
Neville:
Hannah sleepily kissing him on the cheek while he organizes stuff for the DA and Ginny plans
Dumbledore awarding him points for standing up to Harry, Ron, and HermioneHis grandmother being proud of him for being accepted to Hogwarts
The moment he stands up to Voldemort and realizes he isn't as scared as he used to be