When Richard visits young John Locke, he asks him to identify the items that belong to him, even though he never saw them before. This is the same way that the fourteenth Dalai Lama was found; monks showed him several items, of which he positively identified several that had belonged to the previous Dalai Lama by saying they were his. This convinced most Buddhists that he was the reincarnation of the former Dalai Lama, and therefore their rightful spiritual leader.
When Richard comes to visit John, he is playing backgammon. This is the same game that John taught Walt to play and is shown randomly throughout the series. When Locke first teaches Walt to play the game, he explains that it is a game of "dark and light, good and evil." This is another reference to what happens with the constant struggles on the island between the Others, the 815 survivors, and the people on the ship.
When Richard visits John as a small boy and "tests" him, Richard sets a comic book on the table among the items for John to choose from. The comic book is a reference to the island with the caption "Mysterious Land" on the front.
Mittelos, the summer camp that John's teacher tells him to look into, is the same name as the company that recruited Juliet in Not in Portland (2007). Mittelos is an anagram for "Lost Time" or "Lost Item." Also, "mittellos" (with doubled l; from "Mittel-los" = "ohne Mittel" = "without resources") is a German term that translates to "destitute."
There is a 'Geronimo Jackson' poster in John Locke's (as teenager) school locker.