What kind of food did soldiers eat in WW2, specifically 1945?

Soldiers of most nations had various kinds of packaged rations. The US for example had rations classified by letters of the alphabet -

A-ration: Garrison Ration. Fresh, refrigerated, or frozen food prepared in dining halls or field kitchens. The most valued of all rations.
B-ration: Field Ration. Canned, packaged, or preserved foods normally prepared in field kitchens without refrigeration.
C-ration: Individual Ration. A complete pre-cooked, ready-to-eat canned individual meal.
K-ration: Individual Ration. Designed as a short duration individual "assault" ration for paratroopers and other specialized light infantry forces. Declared obsolete in 1948.
D-ration: Emergency Ration. Bars of concentrated chocolate combined with other ingredients to provide high calorie content (intended as an emergency ration).

A-rations were generally whatever meat and produce could be obtained locally, so there could be great variety from one theatre of operations to the next. B-rations were generally used when there was inadequate refrigeration for perishable A-rations. The composition of the D-ration did not change much throughout the war but the C-ration developed many variations.

A- and B-rations were only served at bases or established camps in rear areas as they require cooking. C-rations could be eaten hot or cold and required no special preparation or storage, so these could be served almost anywhere.

During the war a new ration for assault troops, the 2,830 calories (11,800 kJ) K-ration, was developed. K-rations were originally intended to be used as short duration rations for only 2–3 days, but cost concerns and later standardization led to its overuse,[1] contributing in some cases to vitamin deficiencies and malnourishment.[1]

There were various other special rations developed for specific circumstances, including:

Type X Ration
5-in-1 ration
10-in-1 Ration
Mountain ration: 4,800 calories (20,000 kJ), discontinued 1943
Jungle ration: 4,000 calories (17,000 kJ), discontinued 1943
The Assault Lunch: Chocolate bars, caramels, dried fruit, chewing gum, peanuts, salt tablets, cigarettes, matches, and water purification tablets; total of 1,500–2,000 calories (6,300–8,400 kJ), discontinued 1947
The Assault ration (Pacific Theater): 28 pieces of assorted hard candy, chewing gum, cigarettes and a chocolate peanut bar[2]
The Aircrew Lunch
The AAF Combat Lunch
Parachute Emergency Ration
Liferaft Ration
Airborne Lifeboat Ration

I kind of hope you are not relying on questions on Able2know to provide you with the necessary research for a novel? (I got the above from Wikipedia).

He's writing a screenplay for his film project, he said.

But most of the questions he posed can be answered easily via the internet ...