...
private Dictionary<string, int> _items;  

public void Startup() {
   Debug.Log("Uruchomienie menedżera magazynu...");
   _items = new Dictionary<string, int>();
   status = ManagerStatus.Started;
}

private void DisplayItems() {
   string itemDisplay = "Przedmioty: ";
   foreach (KeyValuePair<string, int> item in _items) {
      itemDisplay += item.Key + "(" + item.Value + ") ";
   }
   Debug.Log(itemDisplay);
}

public void AddItem(string name) {
   if (_items.ContainsKey(name)) {   
      _items[name] += 1;
   } else {
      _items[name] = 1;
   }
   DisplayItems();
}
...
