Well you could go with the following;
Compo Ration Boxes - can be got from here, could quality and cheap!
https://www.facebook.com/edwardsshed/photos_stream
The cardboard 24 hour ration box
http://www.atlas-repropaperwork.com/shop/24-hour-ration-box
Ammo cans
http://www.ebay.co.uk/itm/1966-Lee-Enfield-Bren-Gun-303-Mk7-Ammunition-Ammo-Box-British-Army-/201349501673?pt=LH_DefaultDomain_3&hash=item2ee15d92e9
http://www.ebay.co.uk/itm/WW2-METAL-AMMUNITION-BOX-DATED-1945-/291465079317?pt=LH_DefaultDomain_3&hash=item43dcac2a15
Brit Jerry cans
http://www.ebay.co.uk/itm/WW2-BMB-Jerry-Can-1944-/151672190437?pt=LH_DefaultDomain_3&hash=item23505df5e5