See the only way this could work, and I am not saying it is a good idea in fact I think it is almost akin to a police state not just telling people what to do, think, buy, eat, etc. They would also have the means to check up that you were obaying the rules as each card or voucher unlike individual notes or coins could be traced back to the individual and a check kept on what it was used for.
But that is not my main point, which is the only way this could work in practice is if the vouchers were only redeemable in a telco or asda or aldi. As well as the obviouse things like food, milk, nappies, etc. You will also need to allow people to buy things like, lightbulbs. Plates, cutlery, medicines like pain killers or threat lozenges. Sanitary wear, condoms, birthday cards, phone top ups.
It will only be the large stores that could supply the range of things, plus have the ready made technology to cope with people buying a range of items off one card. It would still prevent booze, lottery, and smokes. So my real point is this. The tax payer becomes the biggest customer of Tesco, thats not a free and open market, nor is it going to promote competition for everyone. So we subsidise the big companies and watch every single independent shop die or only exist in very rich areas.