Magento 1.8 – How to Clear Session on Browser Close

I didn't really understand what you need, but session in php it's serialized data so you can store in it almost everything, even objects. If you need to store some request data in session you can do this for example in such way:

$session = Mage::getSingleton('core/session');
$session->setData('current_request', Mage::app()->getRequest()->getParams());

and then unset it when you need

$session->unsetData('current_request');

in your example it may be something like

$vhelper->_vendorsession()->setPostData($this->getRequest()->getPost());

and then when you need to unset use unsPostData magic method or unsetData('post_data') to do this

or explain what you need

To know about use of checkout session you should check below link -

http://blog.chapagain.com.np/magento-2-set-unset-get-session/

for more specific answer please share the exact event or requirement when you want to use checkout session.