With help of gurus of C++ (thanks again Meridian, SupSuper, Yankes and Otto for explanations and support) ive add new property into starting conditions block, called needItem. this works very similar to allowedCraft, but it checks, if sending craft contains listed items, and if not, its not allowed to launch (and also land). Here is video demo:
If that feature is wanted for modders, may be it would be possible to add it to OXCE? I can commit it to github. Also im very noob for OOP and C++, so any comments and tips are wellcome.