To add JavaScript or CSS files to the head section of the resulting HTML page, you can add something like this to the _prepareLayout function of a Block class:
$headBlock = $this->getLayout()->getBlock('head');
$headBlock->addJs('somefolder/ask-sheldon.js');
$headBlock->addCss('somefolder/ask-sheldon.css');
As you can see, we can use the layout model to get the head block an use its functions to add files.
This doesn’t work inside of the default constructor of the Block class.
For further information, have a look to class Mage_Page_Block_Html_Head.