One method to ensure enough or maximum energy stores is to consume mostly protein for 3 days followed by 3 days of  high carbs just before the marathon.  By depriving yourself the carbs during the first 3 days you send a message to your body that carbs are needed and when you do finally consume the carbs your body will tend to store more of them than it would without the 3 day protein phase.  Hope this helps.

If you eat a good diet high in carbs for the week before your race you should be fine without actively carbo-loading, particularly if you take in some carbs during the race, through sports drink, gels, etc. There is some debate lately about how effective carbo-loading really is anyway. If you want to "top off your tank", go for a short, fast run the day before the race, and eat a lot of carbs for the next few hours. Realistically you shouldn't need to do that for a half-marathon anyway. Normal glycogen reserves (which is what carbs turn into) are good for about 20 miles. You're only running 13.1.

Len