No citrus or tomato; I'd avoid anything with corn or corn products to avoid excessive chances of tumors. Whole grains like oats, barley, and wheat are good. They have a good balance of proteins. Supplementing the diet with corn-free dog kibble a few times a week, about a lump per mousie, will add protien, fats, and vitamins. Fresh foods like spinach, carrots, bananas, cooked potato or pasta or rice are all good. I use dried fruit because it won't go bad and likes likely to cause digestive problems. Mousies riot over a very small chunk of dried bread or dry breakfast cereal. I use dried because some mousies have trouble with live yeast. My pregnant and nursing does get dry cereal dipped in all natural yogurt. Avoid feeding much of anything sweet as it can cause diarrhea.
Mousies will eat almost anything if they're hungry and they are like children in that they will eat things that aren't good for them instead of the healthier stuff if you let them. Peanuts, sunflowers (and other nuts occasionally) can cause allergies that show as problems with the skin, ears, and eyes. I no longer feed these to my meeces at all. They love safflower seeds so I mix a half a handful into 8 to 10 lbs. of whole grains, as well as a scant half handful of millet a couple of times a week. Some of the English breeders like to give their meeces mealy worms I haven't tried that as it really doesn't add anything to the diet that my mousies alrady get.
Also, I give my meeces filtered water (reverse osmosis filtration) as it's cheap. I figure if I don't drink the tap water they shouldn't have to either.
Meeces couse live quite well on dried bread; I think bread is why the house mouse evolved from other types of outdoor meeces. Who can resist the allure of fresh baked bread, I ask you?