It is possible to customise the output of the RSS feed by configuring JEvents. If you want to go further than this then you can create a template override for the layout.
1. Copy the file components/com_jevents/views/modlatest/tmpl/rss.php to templates/{YOUR TEMPLATE}/html/com_jevents/modlatest/rss.php and edit this copied file
2. Lines 69 - 81 show you how to get some extra fields that you could use in your description. To use any of these simply uncomment this block and append them to $item_description. e.g. $item_description = $item_description .htmlspecialcharacters("<br/>Organiser is:<br/>").$item_organizer;
3. To use any custom fields e.g. images from the standard image addon, you could add these like this:
if (isset($item->_thumbimage1)){
$item_description = htmlspecialcharacters($item->_thumbimage1) . $item_description;
}