Similarly, random acts of kindness only make me happier while I do them, but not afterwards.

I'd count myself as non-neurotypical (and just one data point, of course) but... I agree that RAOK are short-lived - but that short-lived time is fun enough to keep me doing it every so often. I think it also helps to see that kind of thing as a sort of game. Making it fun makes me happy when i do it more frequently (though admittedly not very often).

As to giving to charities. I don't have a regular charity-donation because that is boring. I do, however, randomly give a years-worth of donation to charities that strike my fancy (Sea Shepherds, SIAI, Methuselah Foundation and more)

Perhaps non-optimal from their perspective, but it increases my happiness. Perhaps I'm aiming more at warm-fuzzies than utilons, but it works for me.

One of the other commentors speaks of how to combine this effectively - ie monthly setting aside the cash in "charity account" then being able to donate from this at will - which sounds like a good strategy for keeping it more fun, while still maintaining your pre-committed optimal give-rate.

As to giving in general. I realised a couple of years back that I was a bit of a tight-fist... the kind of person that never bought a round of drinks - and I have been actively working to change that behaviour pattern (eg by shouting lunch for my friends every so often, buying a plate of chips at a meetup etc). Even though I haven't changed very much yet, I have actually noticed a marked increase in happiness - albeit fleeting... there's a nice warm-fuzzy you get from spreading largesse.

...but the long-term effects are that I can now consider myself not to be so tight-fisted. My definition of myself is changing to one for which I have far more respect. That alone is worth the effort (for me).