If you're talking about the Mesolithic and early Neolithic, there were large deposits of flint in the North-East of Ireland (Cushendall and Rathlin Island) and this was traded, in wholesale blocks, throughout Ireland and Scotland, some finding their way as far south as Britain. So flint-tipped spears, knives, harpoons, arrows etc would have been in use.

In areas that lack flint, chert was often used as a substitute. Not sure if this applied in Scotland, or if chert was available.

Mallory's Origins of the Irish is a great source for a lot of this, as is Britain Begins by Cunliffe.