Frozen, dairy and meat (I assume dept 97) is not too heavy, there's just a lot of it. Most of the activity will be in moving around, almost always carrying something, even if it's light.

In dairy, you'll have to regularly lift up to 30 pounds, doing juice and milk. If you fill the eggs, those crates weigh about 40 pounds, but you won't spend all day doing it, just fill it once or twice. About half of dairy is in the 30-40 pound range. The other half (yogurts, cheese) are pretty light.

Frozen is easier. Maybe a couple cases of stuff on a pallet might weigh more than 20 pounds. Most stuff is closer to 10-15 pounds. The biggest issue with frozen is that it's cold, but you get used to it. You won't be in the freezer often.

"Meat" is likely the packaged stuff like bacon, smoked sausages, lunch meat, and snacks like Lunchables and single serve meat and cheese packs. Some of that stuff can be heavy (cases of pickles, bacon), but mostly it's under 25 pounds.

Produce can be heavy and exhausting. Some things are light, like the salads and cut fruits, but cases of bulk stuff (cucumber, celery, apples, lemons, etc) can weigh up to 50 pounds. You'll lift those frequently throughout the day.

Good news is you will get stronger. The first month will be rough though.