With me, it's the premium Taste of Nature nut/seed bars you get in the boxes at Costco (or Kashi granola bars if I'm out of the former). These are very filling and very small and not crazy-expensive if you buy 'em in bulk, so they fit nicely in my front console compartment within easy reach. They're not 'crisp' like many granola bars and you can practically bend them in a C-shape, so you're not dealing with crumbs a lot (although sticky fingers can occur if you're not careful unwrapping them.)
I also take a water bottle of lightly mint-flavoured water, made with Crystal Light mojito mix but watered down to about 20% of regular strength to avoid a sugary blast.
A pic of the bars: https://encrypted-tb...Z-8Hu_Ztz0LLE_w
I find that when I'm out on the water I'm so distracted by fishing that I don't feel the need to eat very much... but as soon as I get to shore I'm famished.