'Cash purchases' means any payments you make for stock to suppliers with whom you don't have an account. As you don't have an account, you have to pay for the goods at the time when you buy them.
It may be the case that many or even all of your stock purchases are Cash purchases. This could be the case if you bought most of your stock from fairs, markets, sale rooms, private sellers, jobbing builders, car boot sales and so on. There's no saying that other dealers will give you account facilities either - many will want paying there and then.
Cash purchases only include items that you buy for resale. They don't include things like tea and coffee you buy for use at work or items such as business stationery. These are covered elsewhere on the cash flow.
Remember to keep safely all the invoices and receipts for Cash purchases, even if the amounts are small. In many cases you may not have any invoices or receipts - private sellers won't normally give you one. If you don't have an invoice, make sure to keep a proper record of the amount paid, the date, the type of item that was purchased and any other notes such as where it was bought.