I wonder if buying truckloads of stuff would be more economical, thus getting MORE overall food for the recipients?
Yup. Quite a difference between buying chicken drumsticks by the 48 pack at Costco and picking them up in 3 packs at the local grocery. Having Amazon and Walmart compete on the food box delivery contract would definitely provide more bang for the buck for both the government and the recipients (unless of course the recipients are not actually in need of food assistance and prefer to convert their snap cards into cigarette money with the aid of crooked store owners).
A couple of years back there was an article in the NYT about the cyclical economy of Woonsocket, RI. The town is in in the dumps and lives on a monthly cycle whenever the food stamp money gets loaded on the cards. The local budget grocer gets truckloads of meat the day before the cards are loaded and sells 'bundles' and 'boxes' of meat to the local food stamp recipients. By week 2, most have eaten their way through the pile and they hit the food bank for basic staples. Not the most efficient way of managing the resource.