Suppose you’re rich, but you’re the kind of rich person who reads Peter Singer; you believe that one person is morally entitled to consume only so much, regardless of how much money they have. Good for you! How should you go about restraining your consumption? Should you look through your budget for expenses that seem particularly wasteful and eliminate those? I say no. The thing to do is simply to give away to charity whatever money you have in excess of what, by your lights, is a justifiable amount to spend on yourself, and then buy whatever bundle of goods makes you happiest subject to the constraint that you have only that amount to spend, just like a person who actually had that amount of money all along would do. If you just look for extravagances to cut, you’re likely to end up spending the savings on something else, and if you don’t you will probably have ended up buying the “wrong” bundle of goods and services.
H Andersson: you are right, but that just affects your decision about how much you can justify consuming.
Chi: You are right that you might want to have insurance against future income reductions, and there really isn't a market for such insurance (for the standard economist reasons of moral hazard and adverse selection), so you might well want to have some precautionary savings. So setting your money aside and giving it away later on is fine. But there is the danger that you will be tempted to spend it, or that your heirs will try to get their hands on more of it than you wanted them to get and less will go to charity.
Why not put the money away in savings, and donate the whole well-invested pile at the end of your life (someone with this mindset is *clearly* smarter than the average investor, right?)? If you assume that there are others in the generation before you that took this tack, you less the damage of delaying immediate charity for the poor, and you have money in case your life is threatened or you change your mind.
When restricting your consumption, you might get strange side-effects. If you assume that I have all my money on a bank-account, free to spend as I choose, the proposed theory holds up. But what if I need to do work in order to earn the money? I would then have to engage in some arbitrary minimum of conspicuous consumption in order to fit in with my given profession. I would also need to buy several goods and services in order to carry out my profession, whose positive side-effects would spill over into my personal life. Thus it would be very difficult to change life-style without changing status and/or profession.
Regards, H Andersson