I suggested that verbs probably wouldn't be a priority if you could only use four words. This is because verbs are action or doing words, as we are taught in primary school. So that means that you can use a gesture to indicate most of them. How many of you teachers have never done a lesson on the present progressive using miming and the question "what I am doing?". The students have to answer, "you're riding a bike", you're having a shower" etc. You get the point.
If you were travelling in Mongolia and nobody around spoke a word of English and you couldn't speak a word of Mongolian, what would be your word number one to learn? I think we can learn a valuable lesson from babies. Generally a baby's first word is mama or papa - not that useful for travelling adults!
But what comes next? Baby wants something that he can see, but doesn't have any vocabulary - so very quickly he learns an incredibly useful word that he can use in conjunction with pointing - THAT!
Now there might ten different translations for the word 'that' in Mongolian, I have no idea. Even so, if you choose one of them that relates to objects or things in general, then you can go into a shop and ask for something to eat - something essential for your survival.