What is ironic about the food bought with the vouchers?

From the text:

"Karen relents. I can't have cash, but she'll make a call and I can pick up a food voucher at a South Portland Shop-nSave. What would I like for dinner?

The question seems frivolous or mocking. What do I want for dinner? How about polenta-crusted salmon filet with pesto sauce and a nice glass of J. Lohr Chardonnay? But Karen is serious. I can't have cash, which, God forbid, I would blow at a liquor store, but neither can I have any old food item that might appeal."