I mean, what was he imagining himself to be? A hunk of cheese? A can of soda?

Yes, I think it was "a can of soda," which introduces the Coca Cola motif.

I was never moved by Leonard either. I was bored by both his story and the actor himself. Sometimes I wonder if this blandness was intentional on the part of the show's writers; maybe Leonard's unremarkable-ness is part of what makes him pitiable, part of why he feels no one wants him. But then it sort of feels like I'm doing mental gymnastics to justify the character's boring nature.

I appreciate the role Leonard plays, being a kind of mirror to Don who elicits Don's empathy and thus indirectly leads to Don's awakening to himself and others. But that appreciation is theoretical. I just don't enjoy Leonard.