Get retroactive refunds
If an item goes on sale shortly after you buy it, the retailer might refund the difference. You could get a $20 refund on a dress or a $200 refund on a laptop, so it pays to keep track. You can save your receipts and watch prices yourself, but apps like Earny will do it for you.
The “Price Rewind” perk offered by Citi credit cards monitors prices for 60 days after you make a purchase and gives you the savings when an item comes down in price.