you want to add a carriage return per item that is not null into a single text box?
I assume you have a finite number of items you are doing this for.
You can make one big formula field
(if isnull(table.fieldB) then "" else table.fieldB + CHR(13))
+
(if isnull(table.fieldC) then "" else table.fieldC + CHR(13))
+
(if isnull(table.fieldD) then "" else table.fieldD + CHR(13))
or make individual formulas out of each of the above and then drag and drop them into the text box (like you did with the original fields)