Cavemen should be able to use flint stones to “enchant” clubs, and maybe spears, by embedding them in the club to make it spiky. Their starting flint stones would have to be removed, though, to stop them from immediately getting a club at +7 or whatever the limit of adding flint to it would be. Alternatively, don’t remove it, and make the starting club +7.

Another option is to use obsidian stones for turning a club into a higher-damaging “spiked club” or macuahuitl, and to avoid the issue of obsidian simply not randomly generating in some games, it could be guaranteed to appear at Mines’ End or certain other points in the Mines.