(1) Most dogs will eat anything. Carrion and poop are dietary staples. We personally feed our hounds the cheapest off name we can find. If your dog is picky, fix that now with hunger and variety - just like you would a spoiled child.
(2) Dry kibble has a decent shelf life - it is pretty much corn for calorie, soy for protein, and meat by-product for flavor. A simply ziplock will keep it dry and edible for a year. Not good for LONG term storage, but for a BOB, it will work well so long as your flip it every year or so.
(3) If space is an issue, consider crushing the kibble into powder and mixing it with water into a paste for the dog to eat. A few quick rawhide chews for dental health on the side will make up for the loss of kibbling if it has to be done for a long time.
(4) With a dog that size, you NEED a dog pack - it will consume so much food and water weight it needs to pull its own weight. Train your dog to wear a pack or pull a bike cart now. Then is too late.
(5) Likewise, remember that you dog needs to learn skills for the apoc, just like you do. Make sure your dog has noise discipline, follows basic commands quickly and consistantly, can carry its own load. Going beyond that (watch, track, hunt, attack, etc are directions you might want to consider when it gets the basics down).