My coworker likes to buy me breakfast and/or lunch every day at work. Is it ok for me to reciprocate sometimes?

I don't think you should continue accepting. Especially since i read in comments that he's married...

Of course it is. You're friends and coworkers? It saves a lot of effort compared to calculating and splitting checks all the time. From the other comments I see that he's married so it's clear that the intent is just to be friendly. By all means, pick up some checks.

You definitely need to insist on paying for your own breakfast and/or lunch. Married guys do not foot the bill all year long (which is depriving his wife and family of something), unless he has some serious fantasies and expectations about you and from you.

If you're married... offer to pay once in a while.

if you're single... it's up to you.

You don’t have to, even if it was a woman, nobody forced them to do that. Unless you ask them, that’s different .

Every once in a blue moon, sure...why not reciprocate. Cheer them up a bit too.

I personally would. But that is up to you.

I think you should once in a while.

Yes. Reciprocate. Soon.

It's not a date :)

What is his motive ? There’s always the risk that there might be an expectation of something down the line. There’s generally no “free” lunch (or breakfast). If he’s only doing it as a friend, and you also consider him a friend, yes you might reciprocate. People like your other friend often end up “surprised” when misunderstandings result.