My most recent walk was 8 miles on flatish fell, but leots of boulder hopping in places. We started after lunch, I reduced my basal on the pump by 50% from one hour before the walk until approximately 1 hour before the end and also reduced my lunchtime bolus by half as well. I ate an apple & 2 satsumas on the walk & gave myself just half a unit of insulin. It's easy to do this sort of thing onthe pump, but much harder on MDI, I remember well.
Have a look at this link:
http://www.diabetesnet.com/node/237
Scroll doen to the table, it gives you some idea of the amount of arbs needed for an hour of different exericses. I'm about 150lb, so can be expetced to burn 22 grammes of carb per hour on a 3mph walk, significantly more if it's more strenuous & gets me out of breath at all as normal walking at 3mph wouldn't.
A good plan is to look at the walk, length/estimated time & difficulty, estimate the amount of carbs that your son will use then reduce the pre-meal bolus by an amount which will equate to half those carbs using his usual ratios and add extra fast acting carbs every half hour or so to add up to the total carb expenditure over the whole walk. This assumes that you start the walk within a couple of hours of eating, otherwise he'll be sky high.
I am half way through my first pack of freestyle optium strips (without calibration) and have nad no error messages so far, but I'l know to look out for it now. A call to Abbott has to be the right thing to do.