As I've mentioned before numerous times on the Internet I am autistic. My life definitely made an improvement after we got our first dog. When she's in the same room as me I feel more comfortable. And if someone else is in the room talking to me, I can focus my attention and look at or pet the dogs, which makes me feel pretty much 110% more comfortable. I don't think I want to ever try to live without a dog in my life ever again. Plus, dogs are the only livng creature that will love you unconditionally.
1. My smartphone
I don't know how I lived before we had smartphones. Being able to pay at the store with my phone is such a timesaver -- much quicker than paying with cash or using a card. Having my access to my calendar (Google Calendar) or my To-Do list (Todoist) at all times is also a convenience that I don't think I would be able to give up. Not to mention some of the other conveniences -- ordering food, checking email or messages, checking the weather, or using Google Translate if you're in a situation involving a non-English language.
3. The Internet
Last but not least, the Internet. I could never survive without this thing. For the second time this post I'm going to mention being autistic. It is incredibly difficult and uncomfortable to talk to people face-to-face. With the Internet I can talk to people by typing on a keyboard. Using text to communicate is my preferred method of communication. Without the Internet, I don't think this would be possible, and I've thought many times how grateful I am that I was born during the time that I was and not decades earlier (lets just try not to think about the fact that decades before I was born, autistic and other people were "imprisoned" in mental institutions for being different).
There's probably more things that I wouldn't be able to live without that I'm not thinking about right now. These three are probably the most important (excluding the life necessities of food and water) and are the ones that I was able to think of right now.