One thing I do is deliberately seek out Public Domain (PD) or Creative Commons (CC0, CC-BY) assets so that I have the rights to both integrate and redistribute those assets.
...and how to give proper attribution for those assets.
In a commercial effort, I would expect to get things properly licensed and signed off and possibly with a legal entity involved. For these game jams and experimental works however, permissive commons assets are great.
With Unity projects, I tend to keep my raw assets and unrelated stuff outside of Unity's generated project directory. Here's what a typical directory hierarchy looks like:
When backing up or archiving a project, I'll just create a 7z archive of the whole thing. Not sure if it's what folks recommend but it works well enough for me.
Hope this helps!