Final answer:
Ben's concern is securing food to survive, as shelter is already obtained and the jacket he's wearing provides inadequate warmth.
Step-by-step explanation:
Ben's primary concern in the given situation is finding food to survive. Although he has found shelter in a cave and is wearing a meretricious, Italian-leather jacket for warmth, the jacket is not sufficient to keep him warm and does not address his immediate need for food. Moreover, Ben's reflections and actions, particularly his contemplation about hunting for food and his acknowledgment of the necessity to do so, highlight that sustenance is his most pressing issue at the moment.