I go for "nibblements" that pack in individual zip bags to get stuffed in odd corners of my carryon. Cut up apples, carrots, celery, turkey pepperoni, cheeses like cheddar, gouda, and/or muenster, shell-less pistachios, almonds, bagels cut in bite sized pieces, various flavors of Cheerios, water. No salads because I'm a clutz and don't want it in my lap. Nothing that needs spreading, ditto. Nothing that requires my bad knee and I stagger to the cafe car. The Cheerios are mostly for eating while bored. Eaten one at a time, they provide flavor and crunch while I'm watching the dark flow by the windows and reading. I try not to sleep at night in coach because I'm one of those "logs thru a sawmill" snorers.
When I get a sleeper, I still bring nibblements. Getting to the club car is easier, meals are provided, but I still like snacks that are more than very sweet, very salty, or very boring.
Edit: yes turkey pepperoni is salty, as are salted nuts. But it isn't boring.