Well, you can use Substitute(List(OrderItems::Item);¶;", " ) but the related items wouldn't appear in excel columns (only one large column). I would think that you want to export from the OrderItems table so your excel would be:
Item# - ItemPrice - Qty- ID Order
A 3.25 3 001
B 9.21 12 001
R .85 1 002
You can then subtotal in excel and even turn it into a pivot table. Oh, and you can include any related Order fields directly in the export as well.