Supplies are the food, water and equipment needed to keep going. Medical supplies, run out of supplies, relief supplies.
In an emergency, supplies is the standard word for what is flown or driven in — aid supplies, emergency supplies. In ordinary use it covers the stock a place keeps: office supplies, art supplies, cleaning supplies. Note supply chain, meaning the whole route goods travel; supply and demand; and that supplies is almost always plural in this sense, while supply on its own is the abstract noun.
1nounsuppliesThe food, water and equipment needed to keep going.
“Supplies reached the valley on about the fourth day.”
2nounstockThe stock of materials a place keeps.
“The office supplies cupboard has not been restocked since March.”
Too few real examples of this word to estimate which sense is commonest.
supplies is stocks of what is needed.