It's tempting to buy lots of inventory so you don't run out and you can take advantage of bulk pricing, but it comes with a downside. Buying inventory is like taking cash out of your wallet and turning it into several different gift cards.
Instead of $20, you now have $5 at Starbucks, a $5 Amazon credit, $5 at the local spice shop, and a single $5 bill left over for any other purchases. If you only actually needed $3 worth of coffee, a $3 kindle book, and $4 in sea salt, then you have $5 sitting around in unneeded product. You could have had double the amount of cash in your pocket to use on a different purchase.