
The first is the WWI - WW2 British Rations FB group - https://www.facebook.com/groups/226602644193336/
This one provides detailed info on British rations of the Great War and Second World War, and is also geared towards re-enactment so there's a lot of info on making and using edible rations. If you're into that sort of thing there's also a fair bit of info on British wartime field cookery and stoves.

The second one is the Australian Military Rations - WWI to Present Day FB group - https://www.facebook.com/groups/162540611070449/
If you love Aussie EFRs, CR1Ms, CR5Ms, PR1Ms and such then you'll see a wealth of info on these from pre-Vietnam era development through to modern menus. There's also a heavy focus on Australian rations of the WWII-era, and this group is THE premiere source for info on Australian WWII and Vietnam-era rations.
Anyone know any other good International/Historic military rations groups on FB?
Cheers!