When you need some pesos to go to the dermatologist, pay someone to fix the air conditioner, or take an Uber across town, tuna is harder to resell than dollars. But the optimal level of tuna in your portfolio is nonzero, in part because sometimes the supermarket runs out, or goes on vacation, or gets shut down by the police for a week, or closes because of the rioting, and having some food in the house is a good idea.