A good tie clip.
I own several of my grandfathers clips that were given to me by my father last year. Two of the clips are over 70 years old. They look great.
And a Fleshlight. Can't forget the Fleshlight.
I can second that. :)
Last week I went through my late grandfather's wardrobe, and I found his grey pinstripe overcoat... It's a beautiful piece, weighs a TON, and I absolutely love it. It was a definitely emotional moment, for me he was pretty much the definition of how a man should bear himself in all things life and style.
First thing after Christmas, I'll take it to a tailor to have it fixed up and adjusted for my measurements. Thankfully I have a similar build as my grandfather in his youth, so it won't need a lot of work.
Fortunately somewhere along the way early in my life I took the path of buying with permanence in mind. Some of the things I enjoy the most are high quality leather and really well made outerwear. Both seem to stand up to any changes in trends and become better with age. I think it is great that you are thinking this way, there is no substitute for having something timeless that has been with you all the way.