Do you plan on drinking what is inside ???

We use a Aluminium Foil Tape when setting out fireworks, it's sold in screw fix and the like. Often used in window seal and the like. You could fake a top with this stuff without much difficulty. Of course it would be sticky on the underneath and wouldn't be the proper way of doing it.

http://www.screwfix.com/p/aluminium-foil-tape-silver-72mm-x-45m/50629

Cheers

Cris