While there are some expectations regarding behavior and what players are responsible for when playing in a tournament, the list of things they must bring or provide is not that long.

The first thing is that players must provide a DCI number if they have one. If they do not have one, they can obtain one at their first event. If at any point a player has more than one, he or she needs to contact WotC customer service and have the information from these numbers combined. You can do so here.

Players must also bring a method to track life total (usually a pen and paper) and are responsible for any tokens, dice or counters they intend to use in a game.

Finally, for constructed tournaments, they need to bring a deck and provide a deck list at the beginning of the event. Most often, tournament organizers will provide blank deck lists for players to fill out and submit.