After such a fantastic effort yesterday, whether you finished the 26.2 miles or not - congratulations on setting out on such a challenge and the hard work is over and now is the time to reward your body.
First take care of any injuries you may have picked up, including blisters (Compeed is great for these) and if you are a victim of the nasty jogger's nipple soreness then icing helps, or if it is broken skin then nappy rash cream or antibiotic cream is the way to go!
Any minor muscle pain/cramping will be expected to reduce within the next 3 - 5 days with some very gentle stretching and movement and also by applying ice 2 - 3 times a day, but of course if you are concerned then a trip to a medical professional is always a good idea. If you don't know of any then always ask friends and go by their recommendations - be it Physio, Chiro, Osteo or soft tissue therapy - it's all good stuff!
Finally, sleep and eat as much as possible for the next couple of days - and good luck in mastering the art of walking backwards every time you go downstairs!