Update session data with new values but keep old ones

[eluser]theprodigy[/eluser]
Just store your food ids as an array in session (I would use database session rather than cookie):

Code:

$this->db->select('ID');
$this->db->from('FoodTable');
$this->db->where('Food',$this->input->post('food'));    
$query = $this->db->get();

$food_ids = $this->session->userdata('FoodID');

if( ! $food_ids )
{
   $food_ids = array();
}

$food_ids[] = $query->result_array();

$data['FoodID'] = $food_ids;

$this->session->set_userdata($data);