If possible, bring along the exact detergent you use at home, or do a test run at home with a travel-friendly detergent. Vacation isn't the best time to experiment with new, potentially skin irritating chemicals. If you're not able to find your favorite in travel size, or don't react well to fragrance free detergent sheets, detergent pods are also easy to travel with, and nearly every brand offers a "free and clear" option. (Just be careful not to smoosh them!). Also, if you don't anticipate needing a large amount of detergent, you can simply pour some in a travel bottle. The same leak proof bottles you'd use for shampoo will work fine for at least a couple loads of laundry. We stay in Airbnbs or other vacation rentals pretty frequently, and it's hard to predict what kind of laundry detergent will be available. I've gotten used to just bringing some of my own detergent along.