Training for a half marathon definitely takes some planning ahead to stay well hydrated and comfortable. Some distance runners prefer hydration packs — small backpacks that carry a liter or more of water, depending on the model. A tube runs from the water bladder over your shoulder for convenient mid-run sipping. Choose a pack made of lightweight, breathable fabric. And be aware that water can take on an odd taste from the bladder materials, so read online reviews and ask friends which brands they prefer. Another option is to wear a belt designed to hold small water bottles during a training run. Carrying water with you will add weight, of course, so that is something to consider.
I don’t like carrying anything when I run. When training for half marathons, I ran a somewhat circular route that goes past my house every 4 miles or so. I planted a couple of water bottles in my driveway, and took big swigs every time I ran by.
On race day, water stations along the route will be enough to keep you hydrated — as long as you don’t skip them. For long training runs, try different ways of hydrating until you find one that works for you.
As for a towel, you could carry a small one in a fanny pack, or tuck one into the waistband of your running shorts or tights; but most runners I know just use their shirts. Sometimes I tie a light sweatshirt around my waist and use the arms to mop up during a run. An absorbent headband or hat can also help keep drips to a minimum. Hope that helps — good luck with your race!