Probably "choose tomatoes". When you talk about "picking" fruit, berries, etc, it typically implies the action of taking them off of the tree or bush. So, if someone told me they were "picking tomatoes", I would assume they are picking the tomatoes off of the tomato plant. Here are some options you could use. "I need to get some tomatoes." "I need to buy some tomatoes." "I need to pick up some tomatoes." "I need to pick out some tomatoes." ("To pick out" something means "to make a selection from the options").

choosing tomatoes - 挑选番茄

These are very similar. I agree with Eddie. I will say that I would tell my family members; - As a reason for going to the supermarket, "I'm going to get some tomatoes." -While in the supermarket, looking down at the tomatoes, deciding which ones look ripe, "I need to choose the best tomatoes." "Pick" is touching and grasping the object. You could pick tomatoes in the garden. You could pick up tomatoes while in the store.

I would “pick up tomatoes from the supermarket”