I looked through the forums and searched the site but could not find any obvious mention of a secure file delete portable app. If it hasn't already been requested or isn't currently in development I would like to formally request it. If it has been requested or is in development then I would like to voice my support for this effort.
I have been using Simple File Shredder by scar5 software on my USB flash drive but I am not married to it. I do not know if it is 100% portable but it works for my purposes.