I am now at the 29k point, which is about 18 miles.
I do not use gels, but all I take with me is water and sharkies:
http://www.shop.runningroom.com/prod...roducts_id=376
I use water after about 45 mins of running, and have 1 sip every 15 mins after that. I would drink more, but I only take 500ml with me. If I took more, it would weigh me down, and I cannot run with a camel pack.
I usually take 1 sharkie every 20 mins after the 45 minute point.
I find after running this distance, my legs are exceptionally sore for the rest of the day, and I always take the next day off.
I do not know what this distance would be like without sharkies, as I have never tried. The longest I have gone without anything, was 17km, around 10.5 miles. However, it was a cold day, no sunshine,etc.