Read the event rules first
Bag sizes, bottle policies and restrictions on battery-powered items vary by venue. Check the actual event's current rules before buying or packing accessories. A compact item is not automatically permitted. Think about the full day, including queues and the trip home, then make a short list of what you will really carry.
Choose comfort with fewer dependencies
For a fan or power bank, check weight, dimensions, charging requirements and the manufacturer's usage instructions. Consider whether you want to hold an item throughout the day or carry it in a bag. For a bottle, check capacity and whether the venue permits it. These details are more useful than assuming every portable product will suit every outing.
Test the carry setup at home
Put the essentials in the bag you intend to use and walk around with it. Notice access, weight and anything that rubs or swings. Remove extras before adding another organizer. Accessories can make a day more convenient, but they do not replace suitable clothing, water access or a plan for changing conditions. Choose for a real outing, rather than an idealized photograph.