This might have been done to death but I just filled a glass with ice and felt immense gratitude that I live in a time after the invention of refrigeration. So top 5 inventions of all time (if anyone suggests Gran Torino IV or something I'll be very disappointed)
My provisional top 5 in no particular order are
Domestication of livestock
Fire-making (which I'd like to include smelting ores etc)
Irrigation and sewage-works (so this could be one, The Aquaduct)
The lever (which ultimately gave us the internal combustion engine)
The Hobby (without which no-one would have been able to think about all this stuff)
I think it's quite clear there are few wrong answers to this. I'm sure lots of people if asked this would automatically say "the internet", but for me this hasn't changed human interaction in a fundamental way, simply made things a lot easier and quicker.