the content.

I suspect (one of) the first word(s) was "autsj" as some meaning of pain/negativity,
because the loudness of expression of pain make it the most likely to be remembered and understood by the "audience" of the word (when there is no direct context for them to understand the meaning from).
Another important word must be food/hungry.

There's a bias here towards the philosopher's error of treating all language as naming. It isn't. It's far more likely that early language would have been about doing - enticing others to act as a group. It's not absence, but acting together, that leads to language. — Banno

Hunting ?
Most other actions (give, follow, sleep, leave) can much easier be communicated by doing; sleeping can be played(pretended?), leaving can be communicated by pointing away.