Walmart does take stuff back without a receipt as long as you return the merchandise within 90 days.
Without a receipt though Walmart will usually issue you a Walmart Gift Card with the amount of the purchase so you can use the Walmart Gift Card to purchase something else in their store.
Without Walmart may not give you cash money back or return money to your credit card or debit card.
Most Walmart stores and other stores require a receipt to return things and get money back.
However is the purchase was not very expensive then you may still get a cash refund for the merchandise you returned even without a receipt.
But if the purchase was more than say $10.00 then you might get a refund in the form of gift card or other store credit.
According to Walmart you'll get an even exchange, a cash refund or a Wal-Mart gift card, depending on the amount of the purchase.