Nuts are great, Peanut butter also, try to get a natural one though if you like it like Whole Earth or Meridian.
Almonds and Walnuts are great, but pretty much any nuts are good as long as they are unsalted/ not sugared.
I get this bag of 'Trail mix' from Coop, it's got allsorts in it, plenty of nuts, and dried fruit, makes an excellent snack. And tend to have a teaspoon of peanut butter most days, as its full of good fats that are great for your heart, helps my endurance with cardio for sure since iv'e started increasing my intake of nuts.