I thought it would be a great place to keep an extra gel. I mean, it would always be there, stoically guarding against the bonk that might sneak up unawares. In that regard, in fact, it might be a good idea.
What I didn't plan for was this: Those little foil packets are NOT indestructible. In fact, even in the somewhat protected environment of a seat pack they can rupture.
It is amazing the damage that can be done in such a small, closed environment. Although it is nice and soft just when you open the packet to eat it, it doesn't stay that way once exposed to the elements. In fact, it turns hard--yet sticky. One might describe it as taffy-like.
Needless to say--though I will say it--I won't be carrying any emergency stashes of energy gel in my seat pack any longer.