Hi,
I have somewhat of a stupid question.
I went for a 2 hour ride outside and it was 30°C (90 F) and only used one of my gels . Is it safe to store the unused one for another ride, or should I throw it away ?
I’m the type of guy who’s always anxious about what he ingests, it’s as close to a phobia as it gets !
I’m sure many here are more adventurous than I am and have tried it. Thanks !
As long as you haven’t opened it, it’s safe to keep.
They will get heated well above 30 deg when they are made.
I agree with @splash as long as it’s a single-serve packet. Like you, I’m also little different about things like this so I would discard any unused gel if it was in a flask.
Agreed that it is safe to use again. Also, FWIW, any gel stored near your body likely got close to 90F regardless of outdoor temp.
I never was, until I pushed my luck too far with cooked meat. Results were disastrous. Now I’m a bit more cautious. 
Thankfully, both sugar and sodium in high concentrations act as a preservative. Since gels are almost exclusively sugar and sodium, they’re essentially self-preserving, even if poured into an open container and left on the counter. A sealed gel is definitely no issue. I’d be more likely to feel comfy reusing a concentrated mixed fuel bottle after a couple days left out than I would a fresh water bottle, tbh.