Package & collect
Package Project... is written end to end and wired to nothing, so there is no way to gather a project's media into one folder today.
A .dna file stores the graph. The media it points at, photos, footage, 3D models, usually lives elsewhere on your drive. Packaging is the operation that copies all of it beside a fresh copy of the project, ready to hand off, archive or move to another computer.
File > Package Project... (Cmd+Shift+P) does nothing. The menu item is real, the routine behind it is complete and correct, and the two are not connected: choosing the item writes a line to the log and stops. The same shortcut is also claimed by the pinned panel, which loses to the menu.
What it would do
Recorded here because the routine is finished code, not a sketch. It asks for a destination folder, copies every referenced asset into assets/ inside it, and writes a self-contained project beside them whose paths point at the copies. Your live project is untouched: it works on a snapshot, and it never moves or alters your originals.
Two gaps are worth knowing before anyone wires it up. It copies only the path parameters of the Image, Video, Gaussian Splat and Model 3D nodes, plus anything linked with Import in the Asset Browser, so audio and imported data files are missed. And it flattens every copy into one folder by filename, so two files with the same name collapse onto one.
What to do instead
Keep media inside the project folder and reference it through $PROJECT, which is what makes a project portable in the first place. See The asset library for the symbolic paths and Projects for the project root.
A Full App web export does gather assets: it collects everything the graph references into the .ntbundle it writes beside the page. That is a delivery format rather than an editable project, but it is the only asset collection that runs. See Web export.