Collective Identity: L decides for Light’s 18th birthday present that he’ll share the title of L with Light and they would be partners.
Convenience Store Gift Shopping: L usually doesn't have to worry too much come Christmas time "Wammy? Technology. Roger? Booze. Near? Puzzle, game, model. Mello? Don't worry, he'd tell you. Matt? Game." Subverted when L finds he can't do that for Light. Shopping for Light is hard because he doesn't have a singular obsession like the others and he has to actually think about what to get him. Also everyone but Light always gives L candy and while L likes candy that means the gifts he receives from Light are always more personal and meaningful.
He Is All Grown Up: L has this reaction when he returns to Wammy's House and sees Light isn't a child anymore.
It Was a Gift: Light gifts L with a silver signet L ring engraved with L's favorite Sun Tzu quote "To Safety of To Ruin" and L gets Light a very fine and expensive watch with Light's favorite Sun Tzu quote "The Commander stands for the virtues of wisdom, sincerity, benevolence, courage and strictness."