For the survivability aspect, I was imagining that these "time travellers" would have a device that could create unlimited free food and water (basically a supp

For the survivability aspect, I was imagining that these "time travellers" would have a device that could create unlimited free food and water (basically a support crew following them). You're right about the strategy, though. If a player could find their way to the coast, and knew their rough latitude (by observing Polaris, for example), their team mate could probably work out which river they had been following, and then guide them back from the coast to some ancient monument.