Using EPPlus with a MemoryStream

None of the other answers quite got me there (the Excel worksheet was always empty), but this worked for me:

using (var package = new ExcelPackage())
{
    var worksheet = package.Workbook.Worksheets.Add("Worksheet Name");

    worksheet.Cells["A1"].LoadFromCollection(data);

    var stream = new MemoryStream(package.GetAsByteArray());
}