No, not similar. You say, "second hand is only used for an instant", but that means using a hand that may have touched something that's not yours, thus potentially infected surfaces. That it's "only for an instant" doesn't help - there's no 3-second rule for virus.
And, in my case, these days, no I don't "usually grab the shopping bags after you’ve already paid, not before", so the "usually" doesn't apply - I shop with one large, sturdy, wide-top (Tom Bihn) shopping bag and my phone (which has my list) in one hand, using (only) the other hand to pick up items and put them in the bag. When I get to the register, that same hand puts the items on the conveyer, and then puts them back in the bag after they're scanned. The hand with the phone unlocks it and waves it over the POS terminal to pay. No contamination between the hands.
If I were to touch my watch with the hand that has been picking up groceries, I can no longer trust that it's clean. We have to take precautions these days.