Food waste does not impact the environment negatively (with perhaps meats being the exception). What's food for you is also food for all the little critters out in the woods. Rodents will eagerly clean up all the burnt oats, the flour will quickly turn to soil, and all other ruined food will attract the attention of one animal or another. Herein is where the real problem lies, feeding wild animals creates problems for humans down the road. When animals become accustomed to finding food near human recreation sites (backcountry campgrounds for example) then they eventually lose their natural fear of humans, and become more comfortable approaching these sites in search of something to eat. With small critters this isn't a big problem, more of an annoyance to future hikers really, getting your camp site raided by squirrels and packrats in the middle of the night. The problem is when you start attracting the larger animals, the ones who are looking for meat scraps.
Whether or not you have to pack your food waste out will depend on what the local rules are. You could bury your food scraps, this leaves the area more sightly, but you aren't going to do any harm leaving little bits in the woods. As far as a whole ruined meal, as long as it's vegetable waste, I'd carry it a good distance away from the trail and fling it out, it'll disappear quickly enough. Burnt meat, I'd either toss into the fire and burn it to ash, or I'd stuff it down a hole. Most holes around here are gopher holes, and gophers are cannibalistic, so they will drag the meat down deeper in their holes.