This has turned into a great thread. I expected the first response to be: "this has been done a hundred times dummy".
Great stuff here, and some sentimental too, so I am going to add to my original post:
"Take care of your knees, you'll miss them when they're gone"
Spend more time listening to your granddad's stories. Wish I had done that x2.
Usually, your wife's questions are not to tell you how stupid you are, but rather to point out all the important details you haven't considered yet.
I should have NEVER sold my 1980 Fiat Spider convertible for scrap just because it needed an new engine.
Give more things away to people who can use and appreciate them. It will come back to you in spades.
The best time I ever had was when my grandpa gave me a box of nails, a hammer, and a whole box of assorted wood cutoffs.
DO NOT use the corner of a flathead screwdriver on a philips screw.
Earplugs, safety glasses and masks are really great inventions. Use them.
Keep dog treats in the shop.
Throw away shop vacuum filters more often then you think you need to.
The guy at Home Depot doesn't know. He has an opinion. That's not the same thing.
In a few weeks my oldest turns 18! 
