This is somewhat related — When I was younger, I used to think of Adam and Eve as essentially ignorant and naive cavepeople, but that's not the image Scriptures provide us with. In fact, I would argue that the most sophisticated people to ever exist are Adam and Eve, and all humans afterwards, though we have progressed in many ways, in terms of wisdom, intelligence, and health, have deteriorated. Adam and Eve knew God, and they knew His creation and how things originally functioned and the use and purpose of things. It's not surprising then, that in the generations that followed, we see some great inventions being made. They built cities and invented instruments.
So, with this in mind, if I had to speculate, I think Adam and Eve would have had some very sophisticated means to do things like cut their hair etc.
As a sidenote, if we can appreciate how sophisticated Adam and Eve were, I think we can better the complexity and severity of the fall. That is, we, the human race, even at the height of our intelligence, still fell into sin. We see this again with Solomon, the wisest man, who was still subject to sin. But like Adam and Eve, and Solomon, we can rejoice in and take comfort in Christ, who bore our sins and restores us to God.
