At the risk of being off topic… Btw, nice topic gnlaera 
… I don’t know what academic work it was that suggested monastics ate leftovers, because I distinctly recall the phrase, “choice curries” being used in Bhikkhu Bodhi’s translations.
Again…I know this is sort off topic… But they didn’t have microwaves (which apparently do something to the dna in food!!) and fridges and freezers.
I imagine they would’ve cooked stuff fresh, daily.
Unless…going back on topic a bit…they used spices and so on to pickle stuff…
I can’t imagine that they’d want to make any being ill through eating spoilt food. This is an issue nowadays. Sure, you may see what looks like a banquet… But what you don’t know is how often the food has be re-heated, when it was prepared, how it has been stored… You take a risk when you put offered food into your mouth these days!! It’s always surprising to me the amount of ignorance there is about food and safety.
Recently, a monk was sent to hospital with food poisoning - so I was told. I imagine the lay people back in the old days wouldn’t have wanted to diminish their Sangha in this way, anymore than we do. Plus, I imagine they valued their monks and nuns and appreciated the enormity of their renunciation - thus, paradoxically, they probably did the best they could, which, I imagine, sometimes was humble fare. But cooked daily - I imagine it was in some ways, a lot healthier.
Perhaps, the food at the time depended on what was locally available. So perhaps more “water based” food nearer the river? My guess would be that the agriculture in those regions today, is probably not too dissimilar to what it might have been in ancient times - India’s famous for being like this, in some respects! Though I think some vegies were introduced - like cauliflower - I think!
EDIT: I think there were practises that allowed monastics to be “dumpster divers” though… 