There are a number of Gallipoli biographies you can access from NZHistory.net that describe a range of men and women who were involved as combatants, medical staff or, in one case, a chaplain.
Two highly recommended published sources that you might want to use extracts from with your class are Maurice Shadbolt's Voices of Gallipoli (1988), which has oral histories from 12 New Zealand Gallipoli veterans and Nicholas Boyack and Jane Tolerton's In the shadow of war (1990), which is a collection of interviews with 11 New Zealand veterans of the First World War, covering Gallipoli and the Western Front.
Images of the key sites on the Gallipoli Peninsula are available from www.anzac.govt.nz. These appear as still images and as panoramic views, and they give you an opportunity to get some sense of what the peninsula and many of its battle sites felt like.
Use one of the personalities to create a fictitious character, and write a diary entry for one day that describes this person's experiences of events at Gallipoli. Try to imagine their mood, fears, frustrations and their hopes beyond their immediate predicament. Think of the sights, sounds and smells this person might encounter. Some of the biographies include diary extracts and will help you get some sense of the tone of these writings. The aim is to try and capture what it must have been like to be that person at that time.