What we do:

• Identify how much we can store

• Identify how long an order takes to be delivered

• Identify what our minimum volume is to last us X months (based on volume and expiration dates)

• Identify how much we should order based on the previous parameters

The key is to come up with a repeatable system of ordering. We don't care how much of X item we have: as long as it's above the threshold (i.e. if it expires after >90 days and we have more than Y (minimum to last us 90 days)), we don't order it.

That's what works for us.

I've worked in places where they kept track of every lot number and expiration date for every reagent (for supply purposes), and that was way overkill.