When we have all of our senses, we often take them for granted, forgetting that there would be absolutely no way to perceive reality without them. The least important senses in the modern world are probably a tie between smell and taste. Although, I can imagine a time when these were necessary to correctly judge whether or not something was safe to eat.
I would argue that the single most important sense, however, is touch. This one is probably taken for granted more than the others, and it actually encompasses so much of our interaction with the world. Unlike the other four senses, which are local, this sense is global. We have countless receptors all over our body sending information to our brain. In particular, these receptors measure temperature and pressure: two critical inputs to safely navigate life.
In truth, sense of touch is not really an appropriate term. We never actually touch anything. inter-molecular lattice of which our skin is composed actually becomes more compact, and resists this departure from the equilibrium that preceded it. It is for this reason that a "push force" is actually an electromagnetic force. When we press our fingertips against something we cannot see, we judge it to be soft or firm based not on what it does, but rather what it does to us. A given force per unit area at the contact causes our fingertips to deform slightly (to strain), and our internal pressure sensors inform us about what we are "touching". When we "touch" other things, weak bonds also form between the atoms on our fingertips and those on the surfaces they are in contact with. This can actually allow us to pull things too via static friction.
