settings->media
this is setting a wordpress itself

at some point i did this here in a development environment but decided against it.
if memory serves me right it was either because it confused the issue for the user or the boxes would have been way too big for the cart, but I cannot remember anymore exactly.

i guess your could try adding this again along these lines so the relevant scripts/styles get loaded on all pages and not only the order page.

you will possibly also have to apply the spinner css/styles again somehow after the car is refreshed . *perhaps* look here https://support.wp-pizza.com/topic/running-your-own-custom-javascript-functions-on-cart-refresh/

anyway , the below might get you going (not tested though and just off the top of my head so to speak)

add_action('wp_enqueue_scripts', 'my_script');
add_action('wp_footer', 'my_footer_script');
function my_script(){
	global $wp_scripts;
	/*get wppizza options*/
	$wppizza_options = get_option('wppizza');
	$style= $wppizza_options['layout']['order_page_quantity_change_style'];
    	
    /*load spinner css on all pages - keep 'order_page_quantity_change_style' to only enqueue once*/	
	$ui = $wp_scripts->query('jquery-ui-spinner');
	wp_enqueue_style('jquery-ui-'.$style.'', "//ajax.googleapis.com/ajax/libs/jqueryui/".$ui->ver."/themes/".$style."/jquery-ui.min.css", false, null);    	
    /*load spinner js*/ 	
	wp_enqueue_script("jquery-ui-spinner");

}
function my_footer_script(){
print'<script>
	jQuery(document).ready(function($){
  		var spinnerElm=$( ".wppizza-cart-incr" );
       	spinnerElm.spinner({ min: 0});/*set min var*/

		spinnerElm.on( "DOMMouseScroll mousewheel", function ( event ) {
		  if( event.originalEvent.detail > 0 || event.originalEvent.wheelDelta < 0 ) { //alternative options for wheelData: wheelDeltaX & wheelDeltaY
		    // down
		    if (parseInt(this.value) > 0) {
		    	this.value = parseInt(this.value, 10) - 1;
		    }
		  } else {
		  	// up
		  	this.value = parseInt(this.value, 10) + 1;
		  }
		  //prevent page from scrolling
		  return false;
		});

	});
	</script>
';  
}

what do you mean by ” the php.ini is in that path” ?

the session save path has to be set in the php.ini….

either create that path or set another one in the php.ini

PS:you do not change the path of THIS session, but change/create the path for ALL sessions.
i.e you need to have/create a *directory* where the sessions are stored

ok,
as of 3.4.1 i added the following filter just before $printerid = $printers[0]['id'];

/**filter as required**/
$printers = apply_filters('wppizza_gcp_filter_printers', $printers, $orderId, $order);

which shuould let you do all your things there and also passes on the $order parameter so you can save yourself the whole new WPPIZZA_ORDER_DETAILS() etc shebang

question for you (as i dont even have a printer).

have you actually tried this code and does it work to select from different printers ?
happy to add this (or similar) if that is the case

please see the shortcodes
https://support.wp-pizza.com/topic/wppizza-shortcodes/ -> **display the users order history**

currently re-ordering is not possible from there (perhaps in wppizza v3)

hooray !

you are right. you cannot do that .
the plugin allows to add toppings to a base so to speak. it does not cater for adding/chaining menu items to menu items (and then adding / substracting toppings for those subitems)