Twilight Tokens are small, numerous tokens used to count out the twilight cost of a card. As the Free Peoples player pays out twilight, it fills the Twilight Pool, and as the Shadow player(s) pay their costs, they take it out of the same. Twilight tokens therefore need to be numerous and easy to grab, as they'll be moved around quite a bit over the course of the game (and depending on the format, you may need a lot of them). Typically, translucent dark grey glass beads work best, as shown to the right.
Due to the number that every dedicated LotR-TCG player should have on them, twilight tokens usually double as burdens and culture tokens, in a pinch.
See Twilight Pool and Twilight Cost for an explanation of the mechanics.