This is inspired by Bruce's thread on Big Spenders (
Link), where it was mentioned by some posters that you often see the same cards over and over again at auctions, but for Bruce, what he buys, he very rarely ever re-sells.
So what cards in your collection are you never planning on re-selling (or if you did hit an emergency financial situation, these would be the very last cards you would sell)? You would also not plan on upgrading these cards because you are happy with their condition or you can't really afford anything higher. Therefore, until you meet your maker, these cards ain't ever hitting the market.
For me, these would probably be my rarest cards where I would think I would have trouble re-buying again if I had to sell. And which meant the most to me of course:
c.1915 RPPC Babe Ruth
1928 Tabacalera #98 Ruth
1934 Japanese Bromide Ruth
1926-29 Exhibits Ruth (Portrait) PSA 5 (not rare, but I love this pose)