Disclaimer this method is not mine nor will I take credit for it

1. Find someone selling free sandwich coupons (http://cfagod.selly.store) this is an example as this is an old shop idk if it's still active 
2. I;d Reccomned buying 10-20 coupons depending on how much you're willing to start out with
3. One you receive coupons go and get sandwhiches from my experience you can get around 8 per trip depending on the manager

4. Once you got your sandwiches take them to school or campus and sell them for $1 or $2 each

5. Profit and repeat steps 1-4 as need