We use panko bread crumbs and an egg, it holds together well without getting too dry or tough.That was some damn fine meatloaf I made. I was so hungry I just ate a couple of slices. I put ketchup in top & thought it really made the loaf.
So who use what fillers? I used bread crumbs on this one, but have used various cracker crumbs, raw oat meal, rice, even put diced spuds in it.
This one got no onions or peppers diced into it. I think they are great except in sammich meat loaf. To me they make it too crumbly for a sammich.