I think this one might help:

xaml:

<igRibbon:XamRibbonWindow 
    x:Class="frmTest_xamRibbonSaveButtonsFromQuickAccessBar"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:igRibbon="http://infragistics.com/Ribbon"
    Title="Test" 
    Height="305" 
    Width="587" 
    ResizeMode="NoResize" 
    FontWeight="Normal" 
    MinHeight="305" 
    Loaded="XamRibbonWindow_Loaded" 
    Closing="XamRibbonWindow_Closing">
 
    <igRibbon:RibbonWindowContentHost>
        <igRibbon:RibbonWindowContentHost.Ribbon>
            <igRibbon:XamRibbon x:Name="xamRibbon" >
                <igRibbon:RibbonTabItem Header="Tab1">
                    <igRibbon:RibbonGroup Id="grpTestGroup1" Name="grpTestGroup1" Caption="Test Group 1">
                        <igRibbon:ButtonTool Id="btnButton1" Name="btnButton1" Content="Button 1" />
                        <igRibbon:ButtonTool Id="btnButton2" Name="btnButton2" Content="Button 2" />
                        <igRibbon:ButtonTool Id="btnButton3" Name="btnButton3" Content="Button 3" />
                        <igRibbon:ToggleButtonTool 
                            Id="chkToggleButton" 
                            Name="chkToggleButton" 
                            Content="Toggle Button" 
                            igRibbon:RibbonGroup.MaximumSize="ImageAndTextLarge"  
                            Click="chkToggleButton_Checked">
                        </igRibbon:ToggleButtonTool>
                    </igRibbon:RibbonGroup>
                    <igRibbon:RibbonGroup Id="grpTestGroup2" Name="TestGroup2" Caption="Test Group 2">
                        <igRibbon:ButtonTool 
                            Id="btnSomeOtherButton" 
                            Name="btnSomeOtherButton" 
                            Content="Some Other Button" 
                            igRibbon:RibbonGroup.MaximumSize="ImageAndTextLarge">
                        </igRibbon:ButtonTool>
                    </igRibbon:RibbonGroup>
                </igRibbon:RibbonTabItem>
            </igRibbon:XamRibbon>
        </igRibbon:RibbonWindowContentHost.Ribbon>
    </igRibbon:RibbonWindowContentHost>
</igRibbon:XamRibbonWindow>

VB code:

Class frmTest_xamRibbonSaveButtonsFromQuickAccessBar
    Private DatasetIs_OK As Boolean = False
    Friend GUI_Items As New System.Data.DataSet
    Friend tblQuickAccessToolbarItems As System.Data.DataTable = GUI_Items.Tables.Add("tblQuickAccessToolbarItems")
    Friend strType As Type = System.Type.GetType("System.String")
 
    'We use it to restore buttons on QuickAccessBar and set IsChecked property for chkToggleButton
    Private Sub XamRibbonWindow_Loaded(sender As System.Object, e As System.Windows.RoutedEventArgs)
        If BuildDataset_ForItemsFromQuickAccessToolbar() Then
            LoadItemsOn_QuickAccessToolbar()
        End If
        chkToggleButton.IsChecked = My.Settings.chkToggleButtonIsChecked
    End Sub
 
    Private Sub chkToggleButton_Checked(sender As System.Object, e As System.Windows.RoutedEventArgs)
        My.Settings.chkToggleButtonIsChecked = chkToggleButton.IsChecked
    End Sub
 
    'We use it to save buttons from QuickAccessBar into application settings
    Private Sub XamRibbonWindow_Closing(sender As System.Object, e As System.ComponentModel.CancelEventArgs)
        If DatasetIs_OK Then
            SaveItemsFrom_QuickAccessToolbar()
        End If
        My.Settings.Save()
    End Sub
 
    Sub LoadItemsOn_QuickAccessToolbar()
        Try
            'Read data into dataset from app settings
            If Not My.Settings.chkToggleButtonIsChecked.ToString.Trim.Length = 0 Then
                Dim stream_reader As New System.IO.StringReader(My.Settings.QuickAccessToolBarItems)
                tblQuickAccessToolbarItems.ReadXml(stream_reader)
            End If
 
            If tblQuickAccessToolbarItems.Rows.Count > 0 Then
                For i As Integer = 0 To tblQuickAccessToolbarItems.Rows.Count - 1
 
                    'We want only buttons that is why we check for 'grp', 
                    'in case user decided to add whole RibbonGroup to the QuickAccessToolbar
                    If Not tblQuickAccessToolbarItems.Rows(i)("TargetId").ToString.StartsWith("grp") Then
 
                        'Restore item on the QuickAccessToolbar
                        Dim newQuickAccessToolbarItem As New Infragistics.Windows.Ribbon.QatPlaceholderTool()
                        newQuickAccessToolbarItem.TargetId = tblQuickAccessToolbarItems.Rows(i)("TargetId").ToString
                        newQuickAccessToolbarItem.TargetType = Infragistics.Windows.Ribbon.QatPlaceholderToolType.Tool
                        xamRibbon.QuickAccessToolbar.Items.Add(newQuickAccessToolbarItem)
                    End If
                Next
            End If
        Catch ex As Exception
            MsgBox(ex.Message, MsgBoxStyle.Critical, "Load Items On QuickAccessToolbar ERROR")
        End Try
    End Sub
 
    Sub SaveItemsFrom_QuickAccessToolbar()
        Try
            'We want to have current state of the QuickAccessToolbar, 
            'that is why - clean an old stuff first
            tblQuickAccessToolbarItems.Clear()
 
            Dim string_writer As New System.IO.StringWriter
 
            If xamRibbon.QuickAccessToolbar.Items.Count > 0 Then
                For Each item As Object In xamRibbon.QuickAccessToolbar.Items
                    Dim tItem As Object = item.TargetType
                    Dim x As New System.Xml.Serialization.XmlSerializer(tItem.GetType)
                    string_writer = New System.IO.StringWriter
                    x.Serialize(string_writer, tItem)
 
                    'We are saving only buttons, that is why we check for 'grp',
                    'in case if user decided to add whole RibbonGroup to the QuickAccessToolbar
                    If Not item.TargetID.ToString.StartsWith("grp") Then
                        Dim nr As System.Data.DataRow = tblQuickAccessToolbarItems.NewRow
                        nr("TargetId") = item.TargetID
                        nr("TargetType") = string_writer.ToString
                        tblQuickAccessToolbarItems.Rows.Add(nr)
                    End If
                Next
            End If
            'Write dataset into app settings
            string_writer = New System.IO.StringWriter
            tblQuickAccessToolbarItems.WriteXml(string_writer)
            My.Settings.QuickAccessToolBarItems = string_writer.ToString
        Catch ex As Exception
            MsgBox(ex.Message, MsgBoxStyle.Critical, "Save Items From QuickAccessToolbar ERROR")
        End Try
    End Sub
 
    Function BuildDataset_ForItemsFromQuickAccessToolbar() As Boolean
        If Not AddColumn(tblQuickAccessToolbarItems, "TargetId", strType, False, False) Then Return False
        If Not AddColumn(tblQuickAccessToolbarItems, "TargetType", strType, False, False) Then Return False
        DatasetIs_OK = True
        Return True
    End Function
 
    Function AddColumn(ByRef myTable As System.Data.DataTable, ByVal colName As String, ByVal colType As Type, ByVal AllowNulls As Boolean, Optional ByVal AutoIncrement As Boolean = False) As Boolean
        Try
            Dim newCol As New System.Data.DataColumn(colName, colType)
            If AutoIncrement And AllowNulls Then
                AutoIncrement = False
            End If
            newCol.AllowDBNull = AllowNulls
            newCol.AutoIncrement = AutoIncrement
            myTable.Columns.Add(newCol)
            Return True
        Catch ex As Exception
            MsgBox(ex.Message, MsgBoxStyle.Critical, "Add Column Into Table ERROR")
            Return False
        End Try
    End Function
End Class

Good luck.

Currently there is no built in save/load functionality in the xamRibbon. You should submit a suggestion for adding this. In the interim you would need to save this manually. You could possibly iterate the Items collection of the QuickAccessToolbar and save out the TargetId of the QatPlaceholderTool instances in that collection and then use that to build new QatPlaceholderTool instances when the application is loaded.