My understanding is that unless they have a (rare) medical condition where they go hypoglycemic, they really can't go to low without us giving them insulin. If I saw something under 40 in an OTJ kitty I might call my vet, but I've seen a few people take a reading on a civvie and get something in the 40s, so I wouldn't worry too much - could just be meter variation, or a meter that runs a bit low (of course 82 isn't too low).
I wouldn't offer any dry food - people show up regularly who had OTJ kitties and started giving them small amounts of dry here & there, and they tend to end up back on the juice. :sad: