history shows that human warriors are quite capable of killing one another on low or shitty rations. Sure, a well fed warrior performs better, yet jerky, water and bread can and will sustain the body if consumed in sufficient amounts. that said, no excuse not to round out yer pack with dried fruit and nuts, and biltong>jerky, rusks>bread for long undertakings imo. Also, depends on timeframe: invention of canned food drastically changed aspects of logistics in warfare, and far-ranging adventurers would surely lug some cans around barring modern tech you see with MRE's, unless they got the lay of the land and can sufficiently hunt/forage(And here environment plays a role---ranging into a desert requires better planning and provisioning than, say, entering a dungeon near a settlement or within farmlands)
then again, depending on moral scruples, you can always shove a goblin on a spit and have a good barbie. Also depends on dungeon, certain creatures will surely have stores of food and drink if they are to sequester themselves underground for any length of time, maybe even mushroom farms and therefore beer/wine, hunting packs roving outside, rat farms etc. dungeons reached by portals/dislocation different, as at times a writer won't bother supplying the inhabitants with a food source... sorta game logic you see in some LitRPG's.
that said, if your adventurers got their shit straight, they'll probably be rolling up with a few mules or porters laden with supplies. can always have folk camped outside dungeon, cooks hunters etc. who then make supplying runs into the depths, maybe even moving up camp as the party progresses.
