I remember seeing a photo from the First World War showing some Seaforth Highlanders (if I remember correctly) wearing either gas-mask bags or haversacks as sporrans in the trenches. As I remember, the bags were rectangular in shape, with a two-button flap. Obviously leather was not the best material to be using in the trenches, so this was a "field adaptation".

I think the photo is in the Osprey book about Scottish units in the First & Second World Wars -- I'll check tonight.

Cheers,

T.