I had this problems in making some of my more plainer boxes, and what not, more interesting. I would probably throw in a bar code somewheres on the box, include hazards placards like "Do not let children play inside container" and such. Also it doesn't hurt to put on "Made on Reach" stamp somewhere's inconspicious. Also having a cargo manifest or "Place only these things in container" stamp doesn't hurt. I got plenty of ideas on how to make stuff like that interesting, but don't go as far as to plaster the container with information, after all it is a box.
I know there's a lot of containers in Halo 2 that have pictures and information on the boxes, that would probably be another good source to get references.