Finally learning exactly why River made all those rabbits, especially the blue and yellow one. It was to remind him of his promise to meet her on the moon... which was surrounded by stars that Johnny and River noticed looked like a rabbit.
The way Neil fiercely tries to prevent Eva from moving River from Johnny's memories in belief that it would make him miserable is very adorable and proves that Neil does, in fact, care.
When Johnny and River are reunited at NASA. Although this wasn't real, it shows that in his mind, no matter where she was, no matter when or how he meets her, he will always fall in love with her, and that despite their communication problems, she was irreplaceable, and there no one else whom he would rather be with.
When Eva and Neil are watching the shuttle about to take off, Neil slowly edges towards Eva and either tries to hold her hand or put his hand on her shoulder. Of course Eva brushes him off...
The idea that in the afterlife, Johnny and River were reunited on the Moon... Just as they promised when they first met.
The dancing scene in the lighthouse. The bathos that happens when they trip over each other's feet make it more endearing.
Meta-example. The Steam version of the game has a lone achievement. It is called "Wish Granted", has the tooltip "send Johnny to the Moon", and a picture of Young River and Young Johnny as the thumbnail.