I just threw away many medications and supplies (most unused) that were were expensive and 10 years expired. Corid, Sulmet (a sulfa antibiotic no longer sold,) Valbazen wormer, Oxytetracycline powder, and Tylan. I would try to find where you can source supplies in a hurry at a local feed store. Most of the things you might need are expensive, but may be sourced that day at even grocery stores. Some things may run out of stock during periods when people are buying chicks at feed stores. Many of the things some people falsely tell you that you just have to give your chickens are not really necessary. Those include ACV, DE, and others. I would have some electrolytes around. You can make some homemade with a quart of water, a tsp of sugar, and a tiny pinch of salt, or use Gatorade or Pedialyte. Vitamins are nice, and those come in some electrolytes. B complex tablets for people are useful as a vitamin when needed. If you are hatching or expecting baby chicks, make sure that you have those for a weak chick, or can get Corid if they have symptoms of coccidiosis. I have never had a case in 13 years. With prices much higher than a decade ago, it is a shame to waste money. Do use clean water every day, and a fresh decent chicken feed appropriate for age. Having a spare heat lamp around might also come in handy.
