Gatherings undo a week faster than any single meal
It's rarely one dish that causes the damage at a party or open house — it's plates that get refilled two or three times without anyone really tracking it. A buffet makes portion size disappear because there's no single "meal" to measure against.
Look at the whole spread before serving anything
Walking the length of the table once, before putting anything on a plate, makes it possible to actually choose — two or three dishes worth eating, rather than a small spoon of everything because it's all right there. Once the plate has ten different things on it, portion control has already left the room.
The snack bowl is easy to lose count of
Nuts and dates sitting out near the drinks table get picked at without registering, because it doesn't feel like "eating a meal." Deciding on a small handful before starting, rather than grazing past it every time you walk by, keeps it from adding up unnoticed over a few hours.
Saying no to a second helping is a skill, not rudeness
A host offering more food is normal, and so is saying "I'm full, thank you" once or twice. A lot of over-serving at gatherings happens because it feels awkward to refuse, not because anyone's actually still hungry.
Bring a dish if the spread usually leaves nothing you'd choose freely
If most gatherings you go to are heavy on fried and sweet dishes, bringing one dish you're happy to eat without limit means there's always at least one option that doesn't require restraint.
Standing away from the table helps more than it sounds like it should
Serving a plate and then moving to sit or stand somewhere else, away from the food, removes the easiest source of mindless refills — proximity, not hunger, is usually what drives it.
The gathering isn't the problem
None of this means skipping the occasion or eating separately from everyone else. It's a handful of small decisions — what goes on the plate first, how many times it gets refilled, where you stand afterward — that decide whether one event derails the week or just becomes one normal meal among many.