Initially though you meant home made gels
- maybe that is possible
what is your technique for pacing - do you map it out before hand with way-points and some allowance for inclines/descents and watch then tells you of deviations ?
seem to be climb at 25k on Richmod VA marathon.
(The sad Aldershot runners case does not appear to be down to any runner safety issue
see - incident on pedestrian crossing.)
Some people do make their own gels, mostly ultra runners who might go through a kilo of the stuff in 30 hours etc. But I'm happy with GU.
The most important part of pacing is getting a realistic goal pace. By far the biggest problem is people going way to fast at the start and then suffering later in a death march. They then totally ignore the feedback their body gave them and put their bad experience down to poor training/weather/feeling sick/hills at the end/not their day. In the first 7-8 miles hundreds of people passed me despite the fact I started right at the 3:05 pace group team, Over the last 1 miles I passed hundreds of runners.
You need to do at last one half-marathon about 4-6 weeks before the race, and doing a second half or a 10 K earlier helps. You can use that along with how well various key training runs such as Lactate Threshold runs and fats long runs to help make a prediction. There are many online calculators that can give you a conversion, but they are tuned to runners averaging over 70 miles per week with many years experience.
When it comes to the race you want a fairly even effort all factors being equal. That means you need to slow down on the uphills. On th downhills there is temptation to bank time but it is more important to bank energy. You can bank some time, no need to force yourself too slow, but use the down hills to recover, lower your heart rate a little and save energy for when it matter.
An ideal paced marathon has close to even splits, slightly negative. That is the 2nd half is slightly faster than the first, assuming both halves have the same topology. On Saturday's race the 2nd half has a lot more hills and the the 1st half has a big downhill at mile 8. That makes a negative split a lot harder. But my pace plan was still to ensure the first half was run at a very comfortable pace. Going a few seconds a mile too fast over the first easy 10 miles would cost me dearly over the last 6-8 miles - as witnessed by the hundred of people who passed me earlier only to crash and burn once they had to content with the hills and wind in the middle. You are much better getting to mile 6 1-2 minutes slower than planned than 30-60 seconds faster than planned. You can always make up time at the end of a a marathon, you can never make up for the burned energy of a badly paced start.
I did some homework before racing. looked at the map, especially the inclines, looked at google earth, drove the course and looked at last years data on Garmin to see where my Heart rate increased. I printed a pace band which i looked at just a few times to check I wasn't too fast. You can download some course specific pace bands that take into account the hills, but these are fairly pointless IMO. You need to run the hills based on effort not pace. A hill later in the course will have a bigger impact. You need to keep your heart rate under control on the hills, regardless of whether your watch is saying you are going 30 seconds too slow.
If you have paced correctly with a smart goal then somewhere in the last 10K you may be able to increase the pace, or collapse just passed the finish line like i did Saturday. If you do it wrong then you can loose a huge amount of time, suffer massively and get to the finish knowing you screwed thing up.
Over the last 10K you need to really fight the pain. One mental trick is what I call fishing. Imagine casting out a fishing line to the next person in front and then try to slowly reel them in. I imagine pulling in a line or rope one hand over the other as I very slowly pull in the person and pass them. Line up your next victim and try again. This passes some of the time and helps you escape the pain and the signals form your brain telling you to stop, it increases your pace just a little, and gives big mental rewards as you count up how many people you pass running. try to keep good form, head up. Visualize yourself crossing the finish line and no matter how bad it feels there is no way on earth are you going to slow down now.