Set Boosters are the best packs to open just for fun, containing gorgeous art cards and the opportunity to explore the set. With a full display, players can explore a varied amount of breathtaking card treatments and build on their existing deck strategies.
30 The Lost Caverns of Ixalan Set Boosters
12 Magic: The Gathering cards per booster
1-5 cards of rarity Rare or higher in every pack
1 Art Card (foil-stamped Signature Art Card replaces the Art Card in 10% of Boosters)
3-7 Uncommon cards
3-7 Common cards
1 Land card (Traditional Foil in 20% of packs, Full-Art Land in 33% of Boosters)    
1 Traditional Foil card
1 token/ad card, Helper card, or card from "The List" (a special card from Magic's history or Universes Within card—found in 25% of packs).