Tennis Bag Check for Tournament?

You sound well prepared. A lot of people don't put enough thought into what's in their bag and end up forgetting something. Extra strings are a good idea, especially if you use a brand that is not common. Most pro shops have string, but may not have your brand. Bananas provide potium which is an essential nutrient to prevent cramping during activity. Your pocari sweat may have plenty of potium, but check the label to be sure. If not, it won't hurt to throw some bananas in your bag. I don't like bananas, but I carry a jar of almonds which are also high in potium (and less likely to get squished in a crowded bag). Other than that, sounds like you have everything.