Always make sure you hydrate when running around a con! It may sound like a no-brainer, or something that would be more appropriate for an athletic event, but cosplay can be more taxing that many realize! Walking miles around a convention floor in regular, comfortable, and light clothing would be taxing on any given day, but with the crush of people and heavy fabrics/armor holding in the heat, it's a recipe for dehydration. In many costumes, you end up marinating in your own sweat (...It's gross), with no way to replenish the lost water.
And no one wants you collapsing.
I know there's always so much to do, but it's important! Whether smuggling in water, building in storage to your cosplay, budgeting for the super-pricey food vendors, or bringing a handler to carry it, water is a must. I know from experience how fast lightheadedness, headaches, and weakness hit you. If not for Jae, I can't say I would have survived this many cons. Dehydration feels awful, and it definitely ruins the con experience. So take time to get a little water (and food) now and then, and it's shocking what a difference it makes.
Side note: Maybe build in a way to use the bathroom...
For more information, here's some symptoms of dehydration.