The recruitment day involved group activities including , paper tower group build, 'black bear test' as well as individual assessments including mechanical engineering basics test, a personal profile presentation and a 1:1 interview.
Make sure you act professionally even though it may seem like a casual atmosphere.
It would also be good to take advantage of opportunities to meet current field engineers to find out what it will really be like. Try to get them to give honest answers - field life can be tough.