The idea that only supply packs allow long rests is intriguing. It should be thought over wether that would be a possible solution for the too-easy-too-much problem of long rests. I cannot grasp all ramifications of such a feature now. I try to avoid long rests as much as possible anyway.
But supply packs are so boring! And I find the mixed economy of supply packs and food messy. If it were up to me, I’d just get rid of supply packs entirely and only use food for resting, and slightly reduce the amount of food found scattered about in game. Not too much as I don’t think that regaining spells, etc by long resting should be onerous, and am happy for the food restriction to be there mainly for flavour (ahem!) but I do think it would feel more meaningful if there wasn’t quite as much food around. Especially as lack of food doesn’t prevent resting entirely.
But I’ve probably already said that elsewhere in this thread, or in another similar one.