Deffo an interesting one. I would normally say flapjack but oats may not suit you
The issue with gels and the like ( i prefer jelly babies) is they are short acting – you need one vevey half hour and you get insulin/ sugar spikes
ideally you want a mix of short and long acting carbs.
As for the isotonic drink – I am assuming you mean a drink with loads of maltodestrin. It has very similar effects to the gels
I’d take TBC up on his offer.
Of course you could go for a low teh option – jam on white bread. Contains a mix of different sugars and carbs, low fibre, low tech!