USB on knoppix running out of space(home/knoppix)

[Werner P. Schulz]

Is there a way other than reflashing?

No! Have a look at principles of recombine. If you delete some packages within a flash disk installation, you'll get only a delete-marking but all remains on the stick.

If I get a 16GB stick, is there a way to save iceweasel bookmarks, cups stuff, etc

You can try the way I described for "Backup". Create a '...tar.gz' from persistent memory content of the 8GB stick and integrate it within the persistent memory of a new 16GB Stick.