A simple Nim-sum game, where each player has to draw a number of pebbles each turn, is easy to implement yet hard to beat. You can also change the difficulty so it's somewhat reusable. The AI is only a few lines of code.

many good ideas!

please keep them coming!

does anyone know of any very ancient / prehistoric games offhand?

The 'purpose' of play is believed to be practice for things later in life when the cost of failure or missed opportunity is bigger.

Maybe you can think about each activity/situation in your game, what core skills would be necessary, and come up with a way to practice those skills through a game where the skills are primary game mechanics (then you just need some goal and suitable environment)? Combine multiple such skills into a single game (could relate to completely different activities in the game).

It might not be realistic, but it could be a nice pattern for players to find (and maybe even educational). The games they play could even act as predictors of what is to come, if you want to add hints like that (like make them pretend everything is on fire before a really hot and dry period). Then make them play a game they call 'cannibal attack' just to disturb the player.

"Pull My Finger" (crude jokes) ....

Throwing rocks at things was an early (pre technology) skill that probably was ENDLESSLY practiced by children.

According to wikipedia the oldest confirmed board games are all dice games. Usually stick dice rather than cube dice, but the idea is the same; so the question is whether you want your culture to have invented dice. The rest of the confirmed ancient games are hopping games where stones or pegs are moved around a grid (or in the case of tic-tac-toe and go they are just placed, not hopped). The non-confirmed ancient games are pretty much all agility games, which might be difficut to implement in your game - foot races, weapon contests including stone and knife throwing, duck duck goose, hand-clapping, hop scotch, tinikling or jump roping.

The 'purpose' of play is believed to be practice for things later in life when the cost of failure or missed opportunity is bigger.

"chunkey" (spear vs hurled stone) and "hoops and sticks" (the lawn darts type game) are the adult and child versions of javelin practice.

Throwing rocks at things was an early (pre technology) skill that probably was ENDLESSLY practiced by children.

hoops and sticks supposedly was a paleo-indian children's game. chunkey is also paleo-indian.

Usually stick dice rather than cube dice, but the idea is the same; so the question is whether you want your culture to have invented dice

you would think that if they had, we would have found at least one "stick die" made from bone, then petrified. ground on three or four sides, with cut marks for 1-2-3 or 4. but nothing. never even heard the remotest mention of it, even in speculative (IE unscientific UFO type stuff) so called "archaeology documentaries".

while lack of evidence is no proof - heck we still have yet to find even one tooth of the direct ancestor of both wolf and dog - there seems to be no evidence whatsoever.

OTOH, i already have the "spin the wheel" game, which is also not exactly "lore friendly" <g>.

i guess a toss the bones (dice) game could be ok.

Usually stick dice rather than cube dice, but the idea is the same; so the question is whether you want your culture to have invented dice

you would think that if they had, we would have found at least one "stick die" made from bone, then petrified. ground on three or four sides, with cut marks for 1-2-3 or 4. but nothing. never even heard the remotest mention of it, even in speculative (IE unscientific UFO type stuff) so called "archaeology documentaries".

while lack of evidence is no proof - heck we still have yet to find even one tooth of the direct ancestor of both wolf and dog - there seems to be no evidence whatsoever.

At the very least, it dates to Ancient Greece.

They've also found some divination ones in Ancient Greece that they think are from 500 BC.

Dice kind of imply numeracy

Usually stick dice rather than cube dice, but the idea is the same; so the question is whether you want your culture to have invented dice

you would think that if they had, we would have found at least one "stick die" made from bone, then petrified. ground on three or four sides, with cut marks for 1-2-3 or 4. but nothing. never even heard the remotest mention of it, even in speculative (IE unscientific UFO type stuff) so called "archaeology documentaries".

while lack of evidence is no proof - heck we still have yet to find even one tooth of the direct ancestor of both wolf and dog - there seems to be no evidence whatsoever.

At the very least, it dates to Ancient Greece.

They've also found some divination ones in Ancient Greece that they think are from 500 BC.

Wikipedia says this about using yarrow stalks for divination systems such as the I-Ching:

"Archaeological evidence shows that Zhou dynasty divination was grounded in cleromancy, the production of seemingly random numbers to determine divine intent.[23] The Zhou yi provided a guide to cleromancy that used the stalks of the yarrow plant, but it is not known how the yarrow stalks became numbers, or how specific lines were chosen from the line readings.[24] In the hexagrams, broken lines were used as shorthand for the numbers 6 (?) and 8 (?), and solid lines were shorthand for values of 7 (?) and 9 (?). The Great Commentary contains a late classic description of a process where various numerological operations are performed on a bundle of 50 stalks, leaving remainders of 6 to 9.[25] Like the Zhou yi itself, yarrow stalk divination dates to the Western Zhou period (1046-771BC)"

Yarrow stalks are conceptually similar to a coin flip, which is basically a 2-sided die.

Dice are actually older than this in other parts of the world though. "One of the oldest known dice games was excavated from a Mesopotamian tomb, dating to the 24th century BC" -wikpedia Dice entry Further, the Egyptian game senet was ayed with dice and was played before 3000 BC, they just haven't excavated any dice quite that old.

There are a lot of interesting games in this book: https://archive.org/stream/gamesofnorthamer00culirich . Some of them would be as anachronistic for 50,000 B.C. (or whenever your game is set) as board and dice games -- any dedicated game technology is probably anachronistic -- but there are lots of examples of games in there that you can play with seeds, bits of bone, etc.