"You know nothing, Jon Snow..."
He remembers those words. She said that a lot, as if to emphasize how little did he know of the world beyond the Wall. Of the whole world, actually. She liked feeling smarter than him, and in that aspect, she truly was.
It was one of the very few things that he had from her. Her memory, the only proof that she had once existed, walked into his life and made him fall in love for the first time. And probably the last. He couldn't keep anything of her, Alliser Thorne, Janos Slynt and all their supporters would see that as a proof that he had switched sides, that he still had a wildling side that couldn't be trusted. It was completely unfair, he knew that, but Jon couldn't allow more rumors to be spread. So, he agreed to not keep anything from her.
Not that it mattered. Ygritte didn't possess much, clothings aside. She had a knife during the battle, but it wasn't with her corpse, so it probably was taken away by one of his sworn brothers. She didn't have anything, but Jon didn't need anything either way. He could still remember her, walking up to him with that smile that could lighten up the world and that fiery hair that had been kissed by fire, and only with that memory could he continue to deal with Stannis, Thorne, Lady Melisandre, and every other particular individual that was now on the Wall that he commanded.
"I know now, Ygritte" he answered to his memory. "Even if it's too late, I know now."