+6 Bag o' Munchkin Level Counters describes exactly what you get in the package: six level counters for use with any of the various Munchkin games. As of May 2012, two sets of six counters exist, with each counter featuring artwork from a different Munchkin base set.

And as is custom for every Munchkin-related doodad, this accessory includes a unique game-related rule, namely that if you have the level counter matching one of the base sets being used in the current game, you start the game at level 2 instead of level 1. Determine who starts with which counter by rolling for high number before the game begins.