Supererogatory Behavior

In class on Monday we discussed a scenario in which two people are stuck in a lifeboat with a limited amount of food.  There is enough food that one (and only one) person could, if they ate all of it, survive until the boat reaches shore.  If the people split the food, they will both die.  We all agreed that, if one person were to offer the other person all of the food, that person would be acting supererogatarily.  Similarly, I think we agreed that if one person took all of the food for themself, without asking the other one's opinion or offering an equal share, that person would be acting selfishly and immorally.  However, apart from these two relatively clear-cut scenarios, the morality of various actions that these people could take are somewhat debatable.  I think it is worthwhile to investigate several possible permutations of this scenario.

Personally, I think that if one person (let us call them P1) supererogatarily offers the food to the other (P2), and P2 accepts, then P2 is acting in a self-interested but not selfish manner.  If P2 refuses the food in hopes that P1 will reconsider and eat the food themself, then P2 is also acting in a supererogatory manner.  If P2 refuses the food on the basis that they cannot sit by and watch another person starve in order to keep them alive, however, they are not acting supererogatarily, but merely self-interestedly.  If P1 takes the food without consulting P2 and P2 fights them for it, P1 is being selfish and P2 is being self-interested.  If P1 offers the food, P2 refuses, and then P1 also refuses (not in hopes that P2 will reconsider, but because they are unwilling to watch P2 die) then P1 is acting self-interestedly.  If the two people offer each other the food, and then decide to split it (either because neither person will take it due to not wanting to watch the other die, or to maximize the chances of both people surviving - after all, a ship might pass and pick up the lifeboat before the boat reaches shore) then both are being self-interested.