Email pampers and tell them that their diapers gave ur daughter a rash. Also tell them that u bought a big box and u couldn't return it cuz it was opened. Lastly, tell them that your doctor said to not use pampers anymore.
They'll mail you a $20-50 visa gift card that u can use on anything. They might send you a coupon if they're stupid and didn't read ur email, just reply and tell them the doctor thing again.
You can also SE anything on amazon. An easy thing for beginners is to live chat them about ur last order, tell them that when u got it, it was broken and u couldn't contact them earlier cuz you were locked out of ur amazon account. If you're lucky, you'll get a refund, but most of the time they'll give you $10-20 promotional credit.
Another thing to SE is starbucks, email them and tell them your drink was bad or something (make up a story, be creative). They'll send you a giftcard. You can also email a bunch of food places, most of the time they'll give you a giftcard or coupons.