You will give the players a target weight and they have to run around collecting things in a short period of time that they think will weigh the target amount. They are not allowed to weigh anything until the end when all items are put on the scale and the total is given. Closest to the target wins. It's best to put a large bowl on the scale and zero it, so it's easier to weigh what will no doubt end up being an eclectic mix of objects.

Scoring is, as always, completely arbitrary, you can award only the closest or award points on a sliding scale. Decide how you wish based on the number of players.

You can have some pre-weighed items on display so players can get a sense of what things will weigh, obviously they are not allowed to use any of these objects.

It amuses me to have something in the vicinity that weighs exactly the target amount and even have a cryptic clue somewhere they could find.