Here are some sick drunk ideas that came to my head:
1. A big plastic dildo sticking out of a hole in the side.
2. cover case in sugary gelatin then run sweaty socks on the gelatin to get good fungal growth. (takes a while to grow and very unhygenic) for added color, suggest using stuff from under finger nails, around sinks and pond water.
3. Buy a pigs rib-cage as a case. (might cost a bit)
4. Keep all essential componets in a big paper bag. with some rough holes in it for ventilation.
5. Paste a small poster of "Glitter" on the side.
6. Stick some meat around the case, so its totally covered. Get some maggots and let them feast away.
7. Puke on it once a day for a week until case in covered in a good yellowish crust. for added effect eat pizza with ham and/or spaghetti before each regurgitation session for a good texture.
8. Bring no case and explain to the judges that its in fact an invisible case.

.... Yeah, I'll just get back to drinking now...
"BLuaaaargh..." *burp* *passes out.*