In reply to goose299:
I'm a bit late to the party here, but recently I've been having a bit of success with a home-made energy gel... espresso or ristretto strength coffee stirred into the base of a white chocolate tiramisu mix* and poured into a 250ml flexible pouch.
*White chocolate tiramisu mix - melt white chocolate in a bain marie, add egg yolks (keep the whites) and stir well, add marscapone and keep mixing with an electric whisk until light and fluffy. Meanwhile, in another bowl, whisk the whites until stiff peaks, fold half into the white chocolate mixture, pour the mixture back onto the remaining egg whites and fold gently together. Spoon over boudoir biscuits soaked in strong coffee and the 40% booze of your choice (whisky or rum for me, brandy also works, I wouldn't recommend anything aniseedy) and placed into little coffee cups or dessert glasses or a big communal serving bowl. Leave in the fridge for at least an hour to set (or don't, it's also delicious when still soft and flowing), dust with cocoa, serve with more of the booze of your choice.
Of course, don't forget to keep back enough of the mix to fill the flask 3/5s or 4/5s of the way (depending on the strength of coffee and the desired strength of the goo), then stir in your espresso or ristretto, pour into your flask, and go for a jog.
edit
My recommendation for a packaged gel, the nicest I've found so far, is the Maxifuel Viper Active Gel, lemon and lime flavour. Towards the end of a particularly hellish jog a while ago, I found myself craving one of these gels stirred into some ice-cold tonic water with a shot of freezer-kept vodka and a couple of frozen lime wedges. Didn't get one, and had to climb up another col for 1400m instead.
Post edited at 14:40