Some cards that you can look for are autograph cards( especially famous players), relic cards( jersey cards ), parallel cards which is when a card is numbered out of a certain number (as seen in the first post). In hockey packs look for rookie cards (especially Connor McDavid rookies) which sell for about $300. Also look for old cards in mint (new) condition. The most valuable baseball card is a Honus Wagner card from 1920 which is worth $ 2 million.