At runtime just set the Caption property to a WideString:

var
  WS: WideString;
begin
  SpTBXItem1.Caption := WS;
end;

At designtime just set the Caption property in the Object Inspector.

The item should be placed on a TSpTBXToolbar with Stretched setted to True, and ShrinkMode setted to tbsmNone.
Just set the item's Anchored property to true, you can use the CustomWidth and CustomHeight properties to set the initial size value.

The item should be placed on a TSpTBXToolbar with Stretched setted to True, and ShrinkMode setted to tbsmNone.
Just add a TSpTBXRightAlignSpacerItem above the item.

The control should be placed on a TSpTBXToolbar with Stretched setted to True, and ShrinkMode setted to tbsmNone.
Drop a control on the toolbar and set the control's Align property to alClient or set the Anchors property to include akRight.

You can custom paint toolbar items and controls using this events:

• OnDrawItem/OnDrawBackground: to custom paint the item background
• OnDrawCaption: to custom paint the item caption
• OnDrawImage: to custom paint the item image icon
• OnDrawHint: to custom paint the item hint

All these events have 2 important parameters: PaintStage and PaintDefault.
PaintStage indicates the current stage in the drawing process.
DefaultDraw indicates whether the control should continue with the default painting after the event handler exits. Set DefaultDraw to false to prevent the drawing of the control after the event handler exits. If DefaultDraw remains set to true, the control continues with the default painting process.

Example:

procedure TForm1.SpTBXItem1DrawItem(Sender: TObject; ACanvas: TCanvas;
  ARect: TRect; ItemInfo: TSpTBXMenuItemInfo;
  const PaintStage: TSpTBXPaintStage; var PaintDefault: Boolean);

begin
  if PaintStage = pstPrePaint then begin
    // Override the default painting, we are going to take care
    // of all the painting here
    PaintDefault := False;
    // Paint the item in red
    ACanvas.Brush.Color := clRed;
    ACanvas.Rectangle(ARect);
  end;
end; 

You have to set the toolbar's FullSize to true and ShrinkMode to tbsmWrap.

To disable the focus rectangle painting on button controls (TSpTBXButton, TSpTBXCheckBox, TSpTBXRadioButton) use the OnDrawCaption event, the focus rectangle is painted after the caption painting is done:

procedure TForm1.SpTBXButton1DrawCaption(Sender: TObject; 
  ACanvas: TCanvas; ClientAreaRect: TRect; var ACaption: WideString; 
  var CaptionRect: TRect; IsTextRotated: Boolean; 
  const PaintStage: TSpTBXPaintStage; var PaintDefault: Boolean);
begin
  if PaintStage = pstPostPaint then
    PaintDefault := False;
end;

Use the SpFocusEditItem utility function located in the SpTBXEditors.pas unit. The first parameter is the editor item, the second parameter is the View where the item is located, normally a toolbar view:

procedure TForm1.Button1Click(Sender: TObject);
begin
  SpFocusEditItem(SpTBXComboBoxItem1, SpTBXToolbar1.View);

end;

This is not done automatically by the control, you have to create the buttons yourself, take a look at the Overview demo.
I choose to leave it to the component user because there are many ways to handle this: scrollers, buttons, popups, chevron, different positions, etc.
You can also use the TabAutofit property to resize the tabs without the need to use scrollers, like Firefox.

In Delphi, margins are used to specify the space around the control, and padding the offseting inside the control.
Padding, Margins and AlignWithMargins properties were introduced in BDS 4

The compound components such as the TSpTBXDockablePanel or the TSpTBXTabControl/TSpTBXTabSet have a Toolbar public property, access this property and use the mouse events of the internal toolbar:

procedure TForm1.FormShow(Sender: TObject);
begin
  SpTBXDockablePanel1.Toolbar.OnMouseDown := MyMouseDownEvent;
end;
  
procedure TForm1.MyMouseDownEvent(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
var
  IV: TTBItemViewer;
begin
  IV := SpTBXDockablePanel1.View.ViewerFromPoint(Point(X, Y));
  if Assigned(IV) then
    Caption := IV.Item.Name;
end;

BACKUP YOUR FILES!!! I've made a lot of changes to decouple it from TBX so it will break your code.
- Removed TSpTBXToolbar.SnapDistance, the floating toolbar has ScreenSnap set to default
- Removed TSpTBXCustomItem.AlwaysSelectFirst, not used
- Changed the TSpTBXSpinEdit.ValueType to TSpTBXSpinType
- Changed the FontSettings property of the toolbar items, if you get this message "FontSettings.Bold, Bold doesn't exist" or something similar when you load your project just click Ignore and change the FontSettings property accordingly (e.g. set FontSettings.Style = [fsBold] ).
- Changed the parameters of the toolbar items OnDraw event. If you get this message "Item.OnDrawItem incorrect param list" just click NO and replace ItemInfo: TTBXItemInfo with ItemInfo: TSpTBXMenuItemInfo
- Renamed TSpTBXThemeType to TSpTBXSkinType
- Renamed TSpTBXThemeGroupItem to TSpTBXSkinGroupItem

BACKUP YOUR FILES!!! 2.0 is decoupled from TBX so it will break your code.
The only changes from 1.9 to 2.0 are in the DockablePanels behavior.
- DockablePanels can only be docked to MultiDocks. When loading a project make sure no DockablePanels are docked to normal Docks.
- MultiDocks doesn't have lateral splitters, you can solve this by adding a TSplitter or a TSpTBXSplitter on the Form.