We've come a long way since the "Dark Ages" when most of the things on this list didn't exist. These are the things and ideas that most of us have become so used to having around that we think we actually need them. It's almost impossible for modern people to imagine what life might have been like before these things were invented. If you think of more inventions that we take for granted besides the ones in this list, please comment.
For the modern person living in an industrialized society, going a few hours without electricity is a scary thought. If the power goes out, we're on the phone to the electric company almost immediately, asking when it will be back on. We rely on it to see in the dark, to keep warm when its cold and cool when it's hot. Some people would die very quickly without it (such as premies in incubators and people with pacemakers). Most people use electricity or at least benefit indirectly from some product of it 24 hours a day.
Yet it is quite true that there was a time when people did not know how to harness the power of electron flow. It has long been held that Benjamin Franklin was the first to truly harness electricity. However, some historians argue that even the ancients knew about electricity (citing the "Baghdad Battery" as an example). Still it is clear that large scale dependence on electricity for daily life didn't begin until after Franklin.
Up until the 1860's, the term "plastic" simply meant something that could be given various shapes that it would then retain. It also meant someone who's ideas were easily influenced. If you had told someone prior to the 1860's that you had made something out of plastic, it wouldn't have made sense to them.
Today however, it's getting harder and harder to find something that is not made from some kind of plastic. Imagine what your surroundings would look like if suddenly all the plastic in the items you see was to vanish! You' likely have nothing but piles of screws, wires and various other little bits lying around. The Internet connecting device you are reading this sentence on wouldn't even exist without plastic.
As far as I know, the inventor of plastic was Alexander Parkes who demonstrated it at the Great International Exhibition of London in 1862.
Since almost the dawn of history, we have been using the wheel in some form or another. It's been so long since it was invented, that no one knows for sure who the inventor was. However, since one cannot simply grow wheels right out of the ground nor hunt them down like animals, someone had to have invented them. Many historians think that the wheel must have been invented in somewhere in Eurasia since use of it was so much more prevalent and advanced there than it was in the Americas, even by the time that Europeans "discovered" the New World.
Most people today wouldn't think of traveling further than a few city blocks without the help of wheels in some way (whether that be bicycle, car, motorcycle, bus etc.) Wheels are also the main form of the gears and pulley systems that allow so many devices to move. Even the CD/DVD tray of you computer wouldn't open without wheels.
We would have only a vague idea of what time it was without clocks. You can kind of guess what time it is by looking at shadows and positions of the sun and moon, but our fast paced modern life requires more accurate measurements than that. Besides the obvious examples of wall clocks and watches (itself a relatively recent invention), you'd be amazed at what else in your life has clocks in it. These include: your TV, computer, cell phone, microwave, electric stove, stoplights, etc.
This is another of those inventions that occurred in so many places at roughly the same time and so long ago that we aren't sure who first invented them, but the clock as we now know it didn't gain widespread use until after the 1500's. Even then, they were not in the private possession of the "common man" until after the Industrial Revolution.
By "computational Devices" I mean anything that can automatically carry out mathematical formulas without step-by-step guidance from a human user. This rules out devices of ancient origin such as number systems, tally sticks and the abacus since those devices are merely tools to keep the human mathematician from losing his/her place. I am talking about devices that do all the work for you once you ask the device a math-based question in some form. This can be anything as simple as hitting the "3" "+" and "4" buttons on a calculator to something as complex as typing in the variables into a computer program that then calculates the flight path of the Space Shuttle.
We've become quite dependent on our computational gadgets such as calculators, computers, automatic timers, sensors in our cars etc. that many people would be hard pressed to do even basic math problems in their head.
Anyone who has trouble seeing clearly has come to rely on corrective lenses of some kind. Whether they are modern-day versions of the eyeglasses that Benjamin Franklin perfected (much debate still exists as to who invented the very first eyeglasses), or whether they are the nearly invisible contact lenses, a huge percentage of people in industrialized countries wouldn't even think of leaving their home without these marvels. Most users of glasses come to think of them as extensions of their bodies and are rather shocked and alarmed when the device gets broken or their eyes become too weak for their current prescription.
This is the unsung hero of modern life. Without indoor plumbing and the waterworks system that it connects to, life as we know it, especially in cities, would be far less convenient and comfortable (not to mention far less sanitary). Plumbing itself goes back to the ancient Greeks, but it was not until the early 1900's that the "average joe" could have a sink and toilet inside his own house.
In fact, in the U.S., there were still families who had to go outside to an "outhouse" to relieve themselves and who had to get water from an outdoor pump as late as the 1940s.
An outgrowth of the invention of the wheel, this device was still considered a "plaything of the rich" as late as the 1890's. The first horseless carriages were steam-powered and the first among them was built as a toy for the Chinese Emperor by a Jesuit priest named Ferdinand Verbiest around 1672.
It wasn't until Henry Ford perfected the mass production line in the early 1900's, that a car began to become affordable to the middle class. Cars did not fully eclipse the use of the horse for transportation until after World War I. In fact, during WWI, some soldiers actually rode into combat on horseback.