Group Wellness/Fitness/Health Challenge Ideas?

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I am part of a local weight loss group on Facebook. We are looking for ideas to get the people in the group a little more involved and one idea was to have some daily and/or weekly challenges. We've done eat 5 servings of fruits and veggies in a day, with at least three servings being veggies and we've also done drink at least 64 oz of water in a day (we've only done two days of challenges so far). The group is pretty diverse, so I want to make the challenges so that everyone can participate in them. Does anyone have any ideas? TIA!!!