Larabars, hands down! They aren't pumped full of artificial things and chemicals (the only things in them are dates, nuts, dried fruit and spices or other add ins like coconut or peanut butter). They're 200-220 calories each and they seriously will fill you up. DH and I took them when we were travelling and we would split one bar a lot of the time just to tide us over between meals. They're also easy to replicate at home if you have the inclination.
"There's no such thing as failure. There's only feedback. Stop judging yourself & start recognizing it for what it is, an entry point for learning. The truth is, if you're not failing then you're not really reaching & really trying. If you don't like the outcome of a situation, learn from it, make corrections & reapproach wiser & stronger until you achieve your goals."