Nearly every hotel is going to have amenities for the shower, but some people prefer their own brands, or additional ones for face wash or sunscreen. Obviously you need to be under 100ml (which is 3.4oz, not 3 oz, but that's a general rule) if you're carrying them on. However with most container options, you usually can't get some of the gel/cream/soap out. I like these as they are silicone so 'squeezable' and they can hang on the water with a suction cup, but most importantly they actually stay air-tight. My rule is to refill these during the first shower when I return from a trip so you're ready to go on the next trip!