XElement xml = new XElement("XML",
    new XElement ("TOKEN",Session["Token"]),
    new XElement("ALL_INCLUSIVE", "0"),
    new XElement("BEACH", "0"),
    new XElement("DEST_DEP", ddlDest.SelectedValue.ToString()),
    new XElement("FLEX", "0")
);

public static class XElementExtension
{
    public static string InnerXML(this XElement el) {
        var reader = el.CreateReader();
        reader.MoveToContent();
        return reader.ReadInnerXml();
    }
}