flash bag

Do you mean "flash bang?"

That's essentially a grenade that makes lots of noise and light.

Never heard of a flash bag.

Flashback would be another possibility.

"He extracted a file from the flash bag on his lap." A secret agent in a field camp in Asia.

flash bag, in earlier days of photography, refered to a bag which photographers used to carry accessories such as flash attachments, bulbs, film, lenses etc. In effect a usually small bag for misc items.

Well, the page isn't in English, but there's pictures. It my look like this:

www.max-jp.com/4degrees/Pouches/para,flash.html