I really wonder if ANYONE at NASA or Space X has actually done the math to find out just how much, food, water, air and other consumables it will take to keep a modest crew of say 3-5 people alive for a trip to Mars and back.
Don't be silly. They're not coming back. They will colonize Mars and grow their crops there. Reproduce and have families. Build cities. it'll be some years before they can build the subway, ya' understand but all good things come to he who waits.