From the main sets, the Overlord and Enduring cycles both strike me as versatile cards that will see some amount of play as they provide strong recurring effects
You could stock up on extra packs for players to open, or you could build your own custom packs that might fit the theme of your Cube for players to crack
Some items let you search for cards in your deck, others let you heal your Pokmon, retreat your Pokmon, or disrupt your opponent
For instance, Voltron decks with Uril, the Miststalker or Dragonlord Ojutai can use their well-protected commander to effectively carry The One Ring to Mordor and reap its villainous benefits turn after turn.
If you have some instant-speed blink around, you could prevent them from casting something important, like a key combo piece, for a really long time
It can be a Goblin token swarm, artifact-based Big Red, heavily Burn, classic Sligh-style midrange control or aggro, Boss-style Red, and more