I'm looking for any books detailing or containing the day-to-day experience of soldiers at war or during military campaigns. I am particularly interested in the Napoleonic era and the First World War but if you know of or have a particular favorite please send it my way. This is reading to inform some writing I am thinking of doing (non-academic). Thanks
You might be interested in The Diary of a Napoleonic Foot Soldier. it covers the experience of Jakob Walter, an infantryman who served under Napoleon on some of his biggest campaigns.
John Keegan's The Face of Battle is the classic, formative work on this and covers Agincourt, Waterloo and the Somme. If you're looking for something more academic there are a couple of good edited collections in the form of Facing Armageddon: the First World War Experienced and A Time to Kill: The Soldier's Experience of War in the West, 1939-1945. Another good one on the Second World War is The Sharp End of War by John Ellis.
The absolute best work for this for the First World War is the work that is nothing short of a collection of firsthand accounts related to a bunch of specific topics.
Hot Blood and Cold Steel: Life in the British Trenches in the First World War by Andy Simpson.