You should not need gels or any other kind of fueling or food if you’re running less than 18-20 miles. I can understand bringing along water, but people taking 2 or more gels even though they’re only running a half marathon are definitely overdoing it.
I guess everyone is different, but I don’t typically bring anything if I’m running a half or shorter. As long as you adequately hydrate beforehand, and you haven’t been starving yourself, you should be fine.