Shopping Cart: loop through products to turn off Flat Rate shipping for certain prods

Using ZenCart for selling tickets to events. I am creating a mod that will turn off the flat rate shipping module if an event is within 7 days of current date (I have a new column in products_description that holds the event date).

I am having a problem writing the loop in my function. Where are the shopping cart product ids kept? Or put another way how do I access the items in the shopping cart - $cart is a global var but I cannot fund docs on it.

Any help getting the products_id out of the shopping cart from within a loop would be great.

I may not have been clear in my previous post but I am stuck on this. Here is the code I am trying to get going.

function flat_option_valid() {
    global $order, $db;
    // for admin always true if installed
    if (strstr($PHP_SELF, FILENAME_MODULES)) {
      return true;
    }
   $products = $_SESSION['cart']->get_products();
   $check_flag = true;
    for ($i=0, $n=sizeof($products); $i<$n; $i++) {
	if ($products[$i]['STS_WillCallOnly'] == 1) {
		$check_flag = false;
		break;
	}
    }   
    return $check_flag;
  }

I have a new column called STS_WillCallOnly in product_description. I added that column to the get_products() function but cannot get the value in the loop.

This function simply returns false if product in the cart has this flag set to true.

I have tried getting $products[$i]['id'] but that does not bring back anything. The loop works - I go through once for each item in the shopping cart so I beleive I am on the right track.

Where did you add your information in the shopping_cart class?