Have a sit down company dinner. Cooking, eating and cleaning are good community activities especially when the food is "community" or "family" style. Italian food goes well.
The majority of the agenda should be no agenda. Give people lots of free time to just chat and connect.
Have alcohol available for those that want to consume. You never want to run out of beer.
Poker is a nice add to any offsite.
A community game -- get people to play something so they get to know each other out of the professional context.

Things I run

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