I won't be able to nurse for a few days, so how much breast milk should i stockpile?

Depends on baby: How much to store depends on your baby's age and overall appetite. To get an idea, try to pump and feed once or twice with bottle, even before you have to. See how much s/he needs/wants and how long s/he lasts between feeds with the respective feed amount. That will give you a best estimate. Remember there are very few reasons not to nurse your baby.