how much food for a feral?

There is a feral cat who comes around at different times - sometimes early in the morning, many times just after dark. Sometimes a couple of days go by before he comes back. How much food should I be feeding him? I feed him canned food (he is picky about the flavor!), but he's usually still hungry after he finishes one full can, so I give him another. When he has finished the bowl full and he's still hungry, he sits by his bowl and looks at me. I don't know if he is fed by anyone else around here, but I'm pretty sure he has a very large territory. Are two cans at a time too much for him?

I don't think so, if he's not throwing up after he eats. If he'd hunted a rabbit, he'd get at least that much. It just means he doesn't need to eat again as soon.

I'd definitely look into borrowing/renting a trap from your vet or a local shelter. Feeding is a great start, but it's important to make sure they can't father/give birth to any more kitties.

And I would also leave out some dry food. Most strays/ferals are not picky eaters. I just feed my ferals as much as they can eat during the day. I don't put food out in the evening anymore. I have racoons who are just relentless little pigs .

I also would try to trap and get this stray fixed or into a foster/rescue situation. Wouldn't hurt to start making some calls. Much luck

Any chance the feral cat is pregnant? "Quill" was starving when she first started coming around to my "kitchen" (I feed a feral cat colony of around six to eight cats, plus ? those I don't see). Turns out she was pregnant. I couldn't trap her before she delivered. One survived; "Per Stirpes" ("PS" for short) got TNRd last week.
Also, the feral may have worms.