A future missionary is someone exploring the idea of being called to a mission field. You can partner with one by providing the gift of a missionary mentor whose experience provides teaching and training.
You can also partner with future missionaries by covering costs for gatherings and trainings. This offsets the price of retreats and short-term trips that allow them to gain experience to help discern and take next steps toward service. You can even support Friends in other continents as they train and encourage future missionaries.