Generally, when on the water, I like to "take a breather" after several hours of turning a serene and placid pool into something resembling "beer foam", so I often pack a lunch small enough to carry in the back of my vest.
One of my favorite "things" about fly fishing, is to "sit and watch"........ nature, another fly caster, whatever, so the break is two fold for me.
If I'm not packing a lunch, I like nothing more, (when I'm thinking Steak and fries), than to bite down onto a cement like block of hay, grass clippings and barkdust.......held together by sheet rock mud, in the form of a "Power Bar". They don't melt, (usually), and can hold your hunger pangs over until the day's end.
When in my Pontoon Boat, I always take a lunch, anchor somewhere and again.......... take a break from "All that constant hooking, playing, netting and releasing of all those way-oversized huge Trout" that I've been watching the guy in the next boat over, catching while I've gone fishless for 5 hours.
However, if there's a really good hatch on and I can't match the fly from one of the 103 fly boxes in my vest............. I generally will "dine" on something substantial........ by chewing my fingernails to the quick.
There IS one favorite river of mine, that I've yet to be skunked on......... "The Whodathunkit", which has enough of a healthy fish population, that often Bishop and I will enjoy "butter, salt, pepper and lemon juice"........ surrounded by 2 or 3 sizzling Rainbows over a quickly assembled river bank fire.................