I either swap or sell some to buy more!
Told my husband long ago that I had *no* need to buy any nappies, so I would work with the ones I have (either selling or swapping) if I wanted anymore.
And I think I've pretty much kept to that too...tho a couple months back I bought a big bundle of Little Lamb nappies for baby due in April (without having sold anything). Ended up giving them a makeover with lovely bright dyes but in the end decided I wanted something else. So fortunately I sold them on (making a profit too!) and was able to have a bit of a shopping spree on secondhand nappies, which was fun. Not bought anything overly exciting mind, but fun to get "new" things.
Never bought any new nappies, apart from some unused prefolds from ebay (for nearly a rip-off bargain) back before my first baby was born - oh yeah, and a few proraps long ago. Otherwise, all used ones for me. "Reduce, Reuse, Recycle" - right??!