It varies, and is not as many as it used to be due to online booking and print at home.
For a game like tomorrow, maybe 200/300 could be expected. It used to be several hundred more, in our Conference and League 2 days, but buying habits have changed. Add to that the fact that this game has been heavily promoted for some time, and it may well be that walk ups are less than I've estimated, as anyone who thought about going may have already bought a ticket? Against Shrewsbury recently it was a horrible day weather wise and as a consequence our walk ups were very very low. At the other end of the scale, there were times when we had approaching 1,000 walk ups in the Conference days.
Of course all I'm doing is chucking numbers at it as I don't know anything!!!