I can't give to charity like I did before when I was working, especially as a young retiree. Although at death I hope to bequeath some and I hope to be able to help more when I am older and not as worried about my money lasting.
Since I live abroad in a poorer country (Philippines), I have found different ways to help people. These are things that I just could not do before.
Regarding different kinds of opportunities, I got someone's teeth here fixed at my First World dentist who had never visited the dentist in their life. I am good at interfacing with and finding competent local professionals, so I figure that is some value add (in addition to my money, of course). It ended up taking about a dozen visits.
In another case, I knew someone with a lifetime of stomach problems and was able to get them completely fixed forever (required a proper diagnosis and a course of medicine to let the stomach and esophagus heal and then a change in diet along with ruling out some other things). Many poor people simply don't know what to do or can't even afford to figure out what is actually wrong with them. They will live with these conditions as if they are a normal part of life. Another advantage here is the medical care is so cheap and quite decent. For instance, an ultrasound to rule out gall stones as a cause of pain (ultrasound HBT test) was about $20. In both these cases, it was me interfacing with the doctors alongside the patient, it was a bit too much for the patient to fully understand. I would re-explain everything to them later in more laymen's language.
I agree with the poster above who said it is often more useful to give money rather than personally volunteer abroad. I passed on one volunteer opportunity here recently because I judged it to be more of a feel good volunteer opportunity rather than actually helping, even though the organization is inherently good, what they really need are more doctors and not more foreigners to stand around organizing things. I have tried to get a relative who is a GP in the USA to come here for a couple of weeks and I would help organize all his activities in advance to maximize his usefulness.