As others have said, yes! You want to figure this out during training. Go to a sporting goods store and buy a few brands/flavors (they should be about $1-$1.50) and try them out. You just never know what will work for you.
Example: For me personally, I've tried Honey Stingers (too sweet and not available in stores near me, so I'd need to order them online), Hammer Gel (too watery), Clif gel (I forget what I didn't like about them, something with the consistency I think), and Gu (ding ding ding, we have a winner!). Then I tried different Gu flavors - triple berry (just didn't like it), mint chocolate (tasted great but made my stomach burn), chocolate (reminded me too much of frosting) and vanilla (the winner!). Eventually I settled on Gu chomps (similar to fruit snacks) as the favorite fuel for me.
You also want to use training to figure out your pre-/post-race nutrition, hydration strategy, what clothes you are comfortable running in, etc. You never want to try anything for the first time on race day.