Nothing too amazing but I’ve discovered sunflower kernels. They are high in calories (close to 200 calories/ounce iirc), pack really nicely (air is the enemy), chew easily (my jaw gets tired eating almonds) and taste great (to me). A side benefit is they cost $2.99/ pound at Trader Joes.
My new favorite lunch is sunflower kernels poured into a foil pack of tuna along with some olive oil. Very delicious, compact and high in calories.