Fof the gastronomes of the forum.

In 1916 restaurant cars were removed and GER Hotels Department produced cardboard food-boxes. A luncheon box for 1s 6d contained two ham or tongue sandwiches, one mutton pie, one fruit tartlet, cheese, roll and biscuits and one apple.
I think this is probably good value at today's prices; £6.13, although you would probably need an All Line Rover to find a mutton pie nowadays.

At the end of the war with Germany, restaurant car services were reinstated by 1 October in a limited way. Yet by New Year's Eve 1945 the GWR^▸ (Great Western Railway) managed to put roast pheasant, Brussels sprouts, parsnips julienne and potatoes on its menus, preceded by cream of vegetables and concluded with Christmas pudding and ice cream, price 3/6 plus service which is probably a snip at £7.39 in today's prices excluding service.

From Britain's Railways in Wartime by Anthony Lambert.

I just used an on-line inflation calculator to work out the values. Don't have a mental model of values, but there was 30 years difference and the Great Depression in between.

Constant inflation of a high to moderate level is a post WWII^▸ (World War 2 - 1939 to 1945) phenomena. Before that wars were the main cause of inflation and in between prices tended to be stable or fall during depressions - or in the 19th century just bounce around. This graph shows the history back to 1750 - prices around the start of the Napoleonic Wars were pretty much the same as those before WWI over 100 years later.