I dont' think there's a set amount of protein you need to have. You just need to cut out all the items that *could* be the reason you have to do the protein day to begin with.
I usually stick to meats, nothing canned or anything that could have extra sodium. I do eat veggies but not a whole lot of them, that's up to you tho.
I have also noticed that my loss the next day is a bit higher if I finish off my protein day with a big sirloin steak :o)