Nicholas has a total of 5 1/2 cups + 3 3/4 cups = <<5.5+3.75=9.25>>9.25 cups of flour.
To make the cake and cookies, he needs a total of 3 3/4 cups + 8 cups = <<3.75+8=11.75>>11.75 cups of flour.
Therefore, Nicholas will need an additional 11.75 cups - 9.25 cups = <<11.75-9.25=2.5>>2.5 cups of flour to make the cake and cookies.