A continuum of how much they know about the topic and then pairing experts with novices, or experts with experts etc.
Randomly hand out cards/paper with images on such as bunks, trees, zipline, etc. (one on each card). Then get them to find someone with a card that 'goes' with or matches their card.
Imagine a map of your country on the floor - get them to stand where they were born. Either the nearest or the most separated work together.
Take a pack of playing cards - randomly give out the kings, queens and jacks. Pair/team up accordingly.
Stick differently colored dots on delegates or on their place names (if you use them) or on their manuals. (Do we still give out manuals?)
Use lost and found. Gather a bag of (preferably washed) socks - each picks one then finds their pair. For larger groups, pairs join other pairs by size or color to form larger sub-groups.
Alphabetical order of favorite food. Quite nice for discussion afterwards
Have groups get together who's combines years attending/working at camp fall in a specific range.
Find the person who is most like you/least like you. This is a great way to get people talking to each other at the start of the day.
Find the person you know the least in the room/whose job is least like yours or most like yours. Once in their pairs invite them to discuss what they do to encourage participation.