I've only had to have one of those gels once, and that's when I was weak during exercise because I didn't get enough calories in the day due to some medical condition (muh condishuns!) that occasionally makes me nauseated and absolutely kills my appetite. I'm too stubborn not to exercise though, so I take a zofran and deal with it on a bad day. There's no fucking way you should require one for a 5k or 10k if you've actually eaten.