OK so this is my method and I swear by this 100%. It will be a game changer for you and I know as I have amassed considerable experience over the years. The very best thing to wear under your half tights is a fresh pair of depends. This way when you go out for your 5k and you've got all your essentials (GU, hydration belt, etc) if you've got to go from the calorie and liquid intake you won't need to stop at a port a potty.