Pretty much in the order that I acquired and used them:
MIG wire welder. (this saved weeks of labor building custom cars)
Duct tape. (yeah)
My first Mac computer. (A Mac Plus, it was truly an amazing and sucky computer and I learned an immense amount about computing using it.)
The Suzuki Samurai. (Best little 4x4 ever made.)
Recordable CD-ROM. (My first app ran on a CD-ROM.)
Mac OS X (I coded my very first web app on the very first beta version I could get my paws on.)
Netscape Navigator (It too was an amazing and sucky bit of tech.)
Digital Camera (Everyone should put that on their list.)
Cell Phones.
Handheld GPS with Topo Maps (My first was a Garmin eMap. More than anything these increased my confidence in "bushwhacking off trail in the wilderness by confirming I knew where I was. As a result I was able to go further and now I don't worry or think much about it and go wherever I want using a printed topo map. I still bring a GPS but rarely turn it on.)
Super bright LED headlamp (These made a huge difference in my ability to hike at night.)
Linux. (This (and the price) is why I won't be buying another Mac computer.)
A "Supercat" cook stove for backpacking. I shelved several expensive backpacking stoves when I found this.
Raspberry Pi. (I've learned more about using Linux mucking around with these than I ever thought I would or could. I have one on my desk connected to a USB switch and a monitor so I can switch between it and my Mac for work and I will be bringing one with me on a trip this week to use as a portable desktop PC to keep up with things.)
iPhone.
LED monitors and TVs.
Roku (this has saved me a few thousand bucks since I got one. I was able to ditch Dish and DirectTV after years of expensive and crappy service and DirectTV flat out trying to steal from me.)