From Otzi the Iceman to shells from the ocean found thousands of miles inland, there is substantial evidence that trade was both commonplace and sophisticated during the Neolithic period. Trade would likely have existed locally, regionally and inter-regionally (long range). While items would trade through a system of barter, new ideas and perhaps even cultural changes might also have been conveyed by the same early traders.
It might be of greater realism that traders may occasionally encounter the tribe with various materials whose likelihood is related, inversely, to their rarity within a location. And inland tribe, for example, might find a high cost in exchange when trading for shells from the sea, whereas a coastal tribe might find such a trade, cheap.
The game variables might be:
Rarity of items - Difference between item’s typical environmental zone vs. where it is traded.
Proximity to a trade route - Frequency of a trader passing by.
Additionally, we do not know anything about the general marriage practices of Neolithic people, though there is evidence for both exogamy (Marriage outside of your social structure or tribe) and endogamy (Marriage within your social structure or tribe). In addition to traders bringing wears for trade, travelers from other tribes might infrequently appear wishing to join the player’s tribe, i.e. exogamy. Exogamy is a commonplace occurrence in a significant percentage of modern day tribal cultures. Given its benefit to the gene pool, it is probably likely that it occurred during the Neolithic as it did in subsequent recorded periods.