The opportunity to buy additional chips.

The last opportunity players have to buy chips in a "rebuy" tournament.

Some tournaments allow you to buy extra chips after a certain amount of time. The purchase of the extra chips is called an add on. Add on tournaments typically only allow you to buy one 'add on' once after one hour of play, usually during the first break. An add on is available in most rebuy tournaments.

add to the very end; "He appended a glossary to his novel where he used an invented language"

An extra pack that players can either purchase or download that adds increased game modes, scenarios or playing environments to an existing game.

A tour, generally a short one, that can be added to either the start or finish of the tour.

make an addition; "Let's add on to this"