Yes, you are absolutely allowed to bring a Yeti cup or any other reusable water bottle into Disneyland and Disney California Adventure. Disney actually encourages guests to bring their own bottles to stay hydrated in the California sun and to reduce single-use plastic waste. You can fill your Yeti at numerous water bottle filling stations located throughout the parks (look for them near restrooms and in newer lands like Star Wars: Galaxy's Edge). There are only a few specific rules you must follow regarding containers: your Yeti cannot be made of glass, and you cannot bring loose ice inside it through the security checkpoint (reusable ice packs or ice already inside a bottle is generally fine). Additionally, the bottle cannot contain any alcoholic beverages, as outside alcohol is strictly prohibited. Bringing a high-quality insulated cup like a Yeti is a "pro-traveler" move for 2026, as it will keep your water ice-cold for the entire day, even during a heatwave. It also saves you the high cost of purchasing bottled water inside the park, which can be as much as $5 per bottle. Just remember to keep track of your cup, as they are a common item in the Disney "Lost and Found" bins!