I worked on this a little for someone with gluten & soy issues. I had found a "Make your own survival bar" recipe here.
I replaced the packet of orange jello with 1 packet of knox gelatin and 3T of sugar. I experimented with using vanilla as a flavor (1 tsp) and I thought this tasted fine, other people didn't think their oatmeal bars should taste like vanilla. Older daughter thinks they taste good (I agree, at least when they're fresh, not going to unseal them for another 6 mo or so...), picky eater won't eat them (but wouldn't eat a Clif bar either...). I like that there are 1 and 2 year updates on how they stored. I find them bulky, even when I vacuum pack them. I did mine as a series of bars, not one big brick.
As long as you're OK with rotating, I think PB (or Nutella!) have pretty high caloric density, like 2800 kcal/lb. Unless there's a history of nut allergies, PB might be a good emergency food. Crackers are pretty light weight tho, or I'm sure there's some higher-calorie food to spread it on. Due to picky eater, I also have big ziploc bags of "normal" food, and while a lot of it has dyes in it, some stuff (like powdered milk packets, instant oatmeal, instant grits, raisins) don't have dyes in them. Looks like gerber makes a no-dye fruit snack. Ramen noodles don't seem to have any artificial dye. Not sure about the soup base. (My BOB is full of nifty junk food we only eat in case of emergency. It will distract the kids somewhat, I hope, in the event...) All of this, of course, has to be rotated, and is also bulky but it means I'm pretty sure picky-picky preschooler will actually eat something.