Kissing
Sam kept a mental catalogue of how Ed kissed. Soft and slightly teasing after a good day, hard and bruising when Ed had dealt with people he couldn't stand. A gentle good morning/hello just after waking up, provided he stayed the night (which he did more often than not). Smug, cocksure, and confident when he'd done something incredible.
Yes, Ed had a million and one different ways to kiss Sam, but Sam's favorite was the one Ed gave him when Sam showed him the Grid. It tasted like love, like awe, like a "thank you," all combined and sprinkled with happy-joy and splashed with hope. Sam would never forget it.