Maybe something that allows them to grow some food there. Or a composting toilet. Anything that would allow them to stay there as long as necessary.

Edit: ooh and defensive barricades that are hard to take down.

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If you're thinking about a particular encampment that's near you, consider reaching out to ask, because this'll be highly situational. If they are, as you say, well supplied, then getting something they already have plenty of might make their supplies management harder (which ofc, you know, or you wouldn't be asking this question).

Depending on how open your nearest encampment is and your comfort levels in dropping by, going in person to ask is one way. Dropping a message on social media may also be possible: a few of the encampments that I know of would be contactable via social media - even if most of the organising is done on more secure mediums such as signal, there's usually some level of Instagram or similar going on.