Random thoughts, on tablet so forgive the lazy formatting:

Baby carrots instead of, or in addition to, chips. He can use a reasonable amount of dip to augment (1-2 tablespoons max), or lots of mustard.

Sriracha is low cal and can go on a lot of things to give them more flavor, or be used to cut something high calorie (sriracha + mayo for instance). Amazon has 1oz (2 tbsp) dip cups for easy measuring.

Buying individual chip packs might be good, though expensive. Easier to track and limit to one bag per meal.

Diet everything or just water - drinking calories eats through a daily allowance like crazy. Use regular tea as a great filler, sweeten with sugar-free syrups if needed (same with coffee).

You can let him know that most of us go through the "rabbit-shock" phase and that it's normal. Eventually proper portion sizes will become habit and he'll be satisfied with "only" 15 chips.

Smaller plates are a good idea, easier to fill so it feels like more food.

If making a sandwich or burger, leave the top part off while loading the plate so that there is less space for extras. When I make a nice burger, 1/2 of the plate is the top and bottom halves, 1/4 chips, 1/4 baby carrots. Nice full looking plate when I go sit down, but all are healthy amounts.

Drink 1-2 full glasses of water before every meal, and eat slowly. Wolfing down food too fast can make normal portions feel too small, stretch them out.

If you think he can do it responsibly, let him know you can do one or two days a week where you can not really worry about what you have and enjoy the big burger. This isn't advice I give everyone though, it's easy to wreck an entire weeks deficit if they abuse it.

Have him try to identify when he is eating out of habit rather than hunger, which is probably often. Treat those times like a drug addiction - change the people/places/things that trigger the habit, or substitue something else.