Hmm - I would venture to say that most who've posted here have not yet turned 50... ;o) Being 51 I've been there and the thing I really wanted most was a spa day - facial, massage, someone to run the kids to all their various practices, someone to do the laundry, etc. Now, ayear later, I don't really mind being in my 50's but I have to say I would not have appreciated the gag gifts at the time.
That being said, the things that would hit home most for a man would be things that speak to his, ahem, performance. You can buy vitamin supplements that are supposed to boost performance, Geritol, Centrum Silver, reading glasses, prunes or prune juice, "Depends" for men, a cane, borrow a walker or portable commode, preparation H. If he's a huge sports fan something that's directed that way - if he plays softball get him those wiffle-ball sets for little kids that have a huge, fat bat, etc. You can also request information from a nearby cemetery and use it as wrapping paper, or a home-made birthday card, energy drinks, etc.
There are catologs that specialize in supplies that help the elderly - you can find them online I'm sure - also Rite Aid has a great deal of surgical supplies and aids for the disabled - you may be able to find some stuff there.