Minecraft wiki entry for SkyWars, associated text: Creeper Kit: A player spawns in-game with TNT and flint and steel to set off the TNT. This is useful for blowing up other opponents.
Teleporter Kit: The player spawns in-game with ender pearls. This is useful for teleporting to someone else's island right away, though some servers do have a wait time for the ender pearl to be used (so no one is being cheap).
Builder Kit: The player spawns in-game with some sort of building block and a speed potion.
Troll Kit: The player spawns in-game with Cobweb X16, A Knockback weapon, and/or a Note Block or Jukebox