I truly think the solution isn't food but to provide story consequences in the form of complications that discourage long rest spamming. You long rest too much and Lae'zel gets mad at you for taking too long to get to the githyanki patrol, thus you lose relationship points with her, or she outright leaves for a time and you don't see her again until you reach the githyanki patrol. Consequences for taking too long. Not permanent, you can't complete a mission, consequences, but something that makes spamming long rest a bit less desirable and that makes sense from a story perspective.
I can only agree with this.
Story consequences would be the best solution and would make a lot of sense but it won't ever happen and if it is... it'll hurt players that don't like "timed quests" (or loosing a companion for a long time in your exemple)
As an alternative, or in addition to the consequences limitation, because that might get too intensive for Larian to implement, the only other thing that I think would work is having restrictions centered around HP and Spell Slots, which, as a DM, I would do anyway. I never want my players to feel like I'm so restrictive that I'm just trying to kill them, so if their HP and Spell Slots are running low, and they're about to fight a big battle, I'll let them, somehow, find time to long rest so they can keep going.
And so it should be with this game. If your total party HP is less than half, and your spell slots are less than half, your party might need to long rest. Otherwise, you should keep going. You still have plenty left in you to keep up the fight.
It does not work IMO.
What if you cannot rest (because you were lucky and dodged most attacks or don't use enough spellslots) but only have the matriarch left to kill ? Are your only solutions to "try" another combat or to spend your spellslots on the ground ?
Checkpoints is the only answer in my opinion. And supply bags could be some kind of ("mobile") checkpoints.