Washing Machine. Now there are two types of washing machine: the clothes washer and the dish washer. Both fulfil essentially the same function on different commodities. So I'm going to cheat and choose both!
PC. Well I couldn't do above 10% of what I currently do without one. How did anyone run a society, let alone a business, using only a pen, a typewriter and a Roneo machine?
Digital Camera. I like looking at things and trying to make pictures. But I cannot draw for toffee and anyway it takes too long. So I'm glad I learnt photography when young. And then someone invented the digital camera so I don't have to do all that tedious darkroom work.
Spectacles. I've worn specs since I was about 14. That's nearly 50 years (eeek!). They're a part of me and I mostly don't even know I'm wearing them — only true specs wearers will understand the surrealism of trying to wipe your eye only to find you're still wearing your glasses. And I'd be as blind as a at without them.
Biro and Automatic Clutch Pencil. Again I'm going to lump these two together as essential writing implements. I hated the old "dip in the ink-pot pens" as I always ended up with ink everywhere. Fountain pens weren't a lot better. I can't abide blunt pencils but could never sharpen a pencil properly, even with a pencil sharpener and certainly not with a penknife. Good biros and good clutch pencils (I use the Sanford/Papermate PhD range which are so comfortable), while they may not have done a lot for handwriting, have made life so much more amenable. Three cheers for László Bíró and the inventors of the automatic pencil (Tokuji Hayakawa and Charles R Keeran).
So there you have it: seven gadgets for the price of five!
Oh! But wait! I've forgotten the most important gadget of all ... a wife. :-)