First off, you don't have to use parse_url() to retrieve varialbes stored in the url. You can directly access them using $item_id in your code, provided you don't initialize another $item_id variable.
The easiest way to carry variables from page to page is either with cookies or sessions. Sessions are a lot like cookies but provide a little more robustness and flexibility.
To use cookies, simply do:
setcookie("variableName","variableValue","expiration_time");
where variableName can be item_id and variableValue can be the actual id number (if no expiration_time is specified, it is set to expire when the browser window is closed). You can set a new cookie each time an item is added and then retrieve them from the view items page by doing:
$_COOKIE["variableName"];
The only problem with using cookies is that some people turn off cookies in their browsers for security reasons.
To use sessions, call session_start() from each page you wish to carry data to/from. Then use session_register($varName) to register that variable in the open session. As long as you do not call session_destroy(), the open session remains open. You never need to specify a session ID or the likes. PHP will detect if a session is open on the person's computer and start one if not, then register variables you tell it to to that session. Zend has a good intro tutorial to sessions here
