I was told that if I am going to eat just a bite or two of challah, to wash, but don't make the al netilas yadaim bracha. My question is...what if I also want to eat a bite or two of something else (meat, fish)? Does the bracha on the challah cover these things even though I'm not eating a kazayis of the challah?

If in fact you eat less than a k'zayit (about 1 slice of bread) at the meal, you must make a bracha before eating the other foods (R. Ovadia Yosef, Yabia Omer x, Or. Ch. 17, and so it seems regarding Ashkenazim as well, see the Aruch HaShulchan 177, 2 and Magen Avraham ibid, 1 as is clear from Igrot Moshe Or. iv, 41, unless you eat burekas or something like bread, which in this case "joins" the bread, and then you don't make other brachot and do need to bentch Birkat HaMazon). Also, being that you aren't going to say Birkat HaMazon (bentching) on such a small amount of bread, if you eat a kazayit of the other foods you must also say the appropriate bracha achrona.