Mandatory work experience- philosophy/ theology?

You don't need work experience to apply for philosophy (or religious/theological studies), and I can't imagine there's really anything "relevant" in a direct way since those are purely academic fields (unless you're aiming for ministry in your religious tradition after a religious studies degree, although bear in mind a religious studies course in itself isn't training for ministry).
So I would say just find work experience that will be useful for you to get a job later, particularly e.g. a part-time/casual job as a student when you're at uni. Retail, customer service, food services etc are all useful in that regard from a practical perspective. For office based work especially as it's just 3 days I imagine you aren't going to really get much out of it - you'll most likely just be sitting around watching people do stuff while being bored and maybe being given some token busy work task.