This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
You can store multiple objects in a table cell indirectly - through an array or collection. That won't render the way you want though.
For showing two ImageIcons you can use a workaround though - use a custom Icon implementation, and make getColumnClass return Icon.class instead of ImageIcon.class. This custom implementation is not hard (pseudo code):