Sinkholes are a great way to earn both dungeoneering experience and tokens. However, your score and ranking compared to you fellow dungeoneers greatly affect the rewards that you'll walk away with.
At the beginning of a sinkhole, you'll be given an objective to complete. Your goal is to collect and deposit as many resources or totems as possible. Immediately collecting a set of combat gear is highly recommended. Food is usually not needed as monster are low leveled.
Once an objective has been reached, you'll no longer gain points for depositing them - so don't hold on to too many! Once all objectives have been reached, or the time runs out, the game will end.