The phrase "to build a stash" means to save or gather a collection of something, usually with the intention of using or consuming it later. Full definition
Buying used cloth diapers can be a great way to build your stash for much less, and you can get cloth diaper patterns from past seasons that are no longer available new! (mommyscene.com)
It's my go to cover and planning on building my stash with this. (lagoonbaby.com)
During your pregnancy (or waiting for adoption placement), you have the option of building your stash in the last few months and pay in 1/4 or 1/3 installments whichever you choose. (myblossombottom.com)