Imagine if you were a British soldier marching back to Boston from Lexington and Concord and having the colonists shooting at you. What would your thoughts be?
Certainly, thoughts would be internalized and the basic instinct for survival would keep the soldiers' thoughts on their physical activities and needs. Much as in Remarque's All Quiet on the Western Front, soldiers, too, may be most anxious about their chances of returning home to their families and loved ones.
I think the previous posts raise some very good points and thought possibilities. The other topic I immediately thought of was, "I'm hungry." Soldiers on the march, particularly if they're retreating and unused to fighting an enemy that uses camoflauge and unorthodox methods to hide while fighting might not be allowed lots of time to prepare adequate meals, and might be hungry due to the amount of energy they were expending even if they did get time to eat.
British soldiers were not used to fighting soldiers who were awaiting in ambush and who were shooting from protected positions; the English troops were used to fighting in the open and in formation, and their enemy usually fought in a likewise manner. No doubt the soldiers would have been angry about the Colonials' tactics and hoping for a standup fight.
In all honesty, most of the rank-and-file British soldiers were conscripted or coerced into service, and were from the very lowest rungs of British society. They wouldn't be thinking about politics, but rather maybe "what am I doing here?" Many of the soldiers, while subject to rigid discipline, would not have seen combat before, and the chaotic nature of the march back to Boston would have been overwhelming. And yes, as the previous post points out, they would have been completely exhausted- they had, after all, embarked in the wee hours of the morning.
It's a long way for a march, a retreating march at that. The odds are that the automatic thought processes that take over foot soldiers' minds so they can continue, and continue at the right pace, would take over and thoughts would be vague and random. As exhaustion wound deeper, thoughts might very well be about the mechanical process of putting feet in the right way in the right place and holding the right things in the right way.
During the middle a retreat like that, I am sure that the only thing that I would be thinking about was hoping that I did not get shot. I would be thinking hard about whether there was anything I could do to reduce my chances of being shot. I do not think that I would be thinking about any sort of political issues or anything like that. That stuff could wait until I was safe. I would be worried about getting shot and whenever I wasn't worrying about that I'd probably be sad if I saw one of my friends get shot.
In a situation like that, there would be no time for philosophy. It would be all about saving my own life and those of my comrades.