Ben Affleck‘s diet appears to consist of Dunkin’ Donuts and cigarettes — and yet … he’s in tip-top shape, with a dad bod most of us would kill to have.

The actor was picking up his kids in L.A. Monday — specifically, his 14-year-old daughter Seraphina and 11-year-old son Samuel — and he was in complete Papa Bear mode … of the big-rig variety, though, it seems.

Check it out … while waiting with Seraphina in the parking lot, he started rummaging through a backpack and pulled out a giant carton of Marlboro cigs, which was already torn open.

Once Sam showed up and the 3 of them started heading out … Ben had a Dunkin’ coffee cup with him, and it looked pretty empty. We know Ben’s a fan of the coffee/donut brand … so it’s not all that crazy to see him with one of these.

What is interesting … the fact Ben tends to snag fast food pretty often — including a McDonald’s run he made last week, where he had a bag of grub and a tasty drink to boot.

Lop on the fact he’s a regular smoker … and it’s a little surprising Ben’s able to stay in as good of shape as he does. We know the guy’s shredded thanks to a snap his wife, J Lo, shared on Father’s Day — so he must hit the gym regularly to keep things balanced.

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If only we were all so lucky.