Motivation often comes from witnessing the positive results of your actions. A rationalist is especially attuned to this form of observation so it would seem that exercise is the perfect arena for the rationalist to succeed. I run and lift weights and I feel and perform better (disregard looks for now because it's too loaded). If I stop, then I feel and perform worse. Therefore, as a matter of rationalist discipline I will continue to exercise. Eventually, this should normalize into a sense of motivation. For the first timer, exercise might feel like hell but over time a positive and motivating association should develop.
I would illustrate that like this:
exercise (don't like) = feel and perform better (like) => exercise (like) = feel and perform better (like)
And I don't think fat people are irrational, just undisciplined. Developing habits and mental associations takes time. Doing things you don't like over a period of time (which is the same as giving up something you like in the short term) in the interest of a deferred goal is the definition of discipline.
Have you ever noticed that wealthy people often leave money to charity in their wills? It would make sense from a utility standpoint to donate while alive because you can be more involved in the use of your money and ultimately gain the appreciation/satisfaction/utils from the result. You gain no utils when dead and I'm assuming that the prospect of future utility is less valuable than the act of donation in the present. Therefore, why do so many people donate to charity in their wills? A big reason is time. They often don't have time (as perceived by them) to research what they want to give to and therefore just leave it up to someone else. In a sense, it's paying someone to figure out what you care about and then having them donate for you. Another reason is the value many rich people place on money. You call it hit points but to some people it literally feels like lifeblood. In order to make a lot of money, it helps to have this attitude. If they were happy to spend their money (because they care) then they wouldn't be wealthy, would they? There is also the opposite effect where spending money loses all value when all you do is spend it. The only thing that seems valuable is another limited resource, time for example.
However, it's not necessarily an issue of caring but of clarifying what the money buys. If you spend $5 on a burrito you know you are getting a burrito. If you spend $2000 on a diamond ring you are buying...love? The main reason that rich people don't give to charity while they are alive is uncertainty. If they could be sure that their money was going to help a cause that mattered to them then they would be more apt to spend it. That's not such a bold claim. I think that the model of a rational, centralized, data driven charity ala The Bill & Melinda Gates Foundation is an obvious next step in helping people "care". As far as diamond rings for the SO goes...I have no idea.