Many have suggested pets, and that’s not a bad idea. However, it’s possible that he will then worry about what will happen to the pet after he dies. OTOH, some tropical birds would certainly outlive him, and what will you do with one, if he goes for, frex, a cockatoo? I’m most emphatically a pet lover (bred/owned/exhibited Great Danes for 20 years), but I’m not sure about this. You could talk to him about it.
However, I really think that your plan to encourage him to become more involved at the homeless shelter (or add on some other volunteer activity) is the best. I have volunteered at various times in my life when my circumstances permitted, and have always found it very satisfying.
My dad kept from under my mothers feet by doing small DIY tasks for friends, family and neighbours. The combination of being out of the house, talking to other people (boy, did he like to talk …) and being useful appealed to him. He didn’t do anything really strenuous, because he had a mobilty problem, but did the minor jobs that needed doing but professionals couldn’t be arsed to do or charged ridiculous call out fees for.
He cleaned and polished a lot too. He also took up carving and making toys for his grand children (you’re not too old for a hobby horse, are you )
I think the homeless shelter thing is a great idea. It will get him out of the house and interacting with lots of people, which will take his mind off of his loss and keep him from being lonely and depressed.
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