When it came to fuel and hydration I drink water sometimes with an electrolyte tablet in it and use SIS gels and muesli bars to keep me going every 4 miles after the seven mile point. But others on this forum may have better suggestions.
Wise move getting your gait checked.
As booktrunk says just get out there, and dress for the conditions. No excuses - after all it could be raining or snowing on marathon day.