My Hannigram headcanon is that they like to pass time playing mind sports. Chess, memory games, puzzles. I like to think Hannibal is better at mathematics-based games, being so practical, and Will wins intuitively, skipping steps to victory that Hannibal sometimes cannot grasp unless he thinks on it step-by-step to figure out exactly which steps Will skipped over. Hannibal introduces Asian games to him like Go and Mahjong, inadvertently teaching (training) him to read Chinese characters. Post fall, now and then, they will have an abandoned chess board on the table, left halfway, bored or distracted. Will has the “out of sight, out of mind” personality, and while it should bother Hannibal’s sensibilities, and he can never forget it exists in the house, he lets it be.