As Seasoned pointed out, just engage him in light conversation. You could ask him about what cuts of meat are best for certain types of cooking. Or, you can ask the best way to slice a cut of meat. Anything that wouldn't make his boss (if he's around) wonder why the conversation was going on for 5 minutes without you buying meat immediately. This is known as an icebreaker. People seem to think they need to "know" someone's interested without just talking to someone one human being to another. That is the best way. And NOT just for one conversation. Frequently. If he has an interest in you, he will attempt to prolong the conversation, if it's not too busy at work. You could also go sometime when you know it is going to be slow, so he can talk without worrying about looking like he's not doing his job.
I disagree with some of the other posters, as straight men will rarely look at you for 4 seconds without saying anything or at least giving you a "nod" as they recognize you as a regular customer. And they certainly don't do it several times, as they're usually aware that anytime guys lock eyes and don't look away, it could be construed as being "gay."
I don't know what part of the country you live in, because I haven't looked at your profile, but I'm speaking as someone who lived in San Francisco over several decades, and rarely saw a straight man hold my glance, although once, in a supermarket, another brother (meaning, another Black man [I'm Black, in case my icon doesn't show it clearly]) said to a customer, after I greeted him and walked by, that I had a great build. I only know because I passed him again, and he told me he'd said something to a woman who'd been nearby, and she asked him if he was gay. He told her, no, he wasn't, but that I had a great build and he admired it, that was all. And he was comfortable relating the conversation with the woman, but then, in Black culture, we're very pointed: for the most part, we say what's on our mind to each other. I can't speak for other cultures. But back to you: just engage him as a person, not as someone you're interested in maybe having sex with. That always works best (unless you're in a gay bar and you're cruising), and it's a lot easier to be cool and nice to someone and get results instead of approaching each encounter as though it's a now-or-never thing.
And, you could always mention that you need to learn how to cook meat, since you're alone and you're finally getting around to learning how to cook meats, and nobody else is gonna do it for you.
