[Drolefille]

I wouldn't talk about religion itself, but it's ok to say you went on a mission trip or you volunteer with your church. You can leave out the religious part or not, but it's really common on SLU's campus and not particularly frowned upon or exalted. It'll be the activity rather than the religion that they'll want to talk about.

No one should be wearing jeans. Actives will probably wear capris, denim skirts, or black pants. A pattern would be a good way to stand out if you can pull it off, otherwise any similar bottom would work just fine.

As for flipflops, I recommend against unless they're "nice" ones. You don't need to wear heals, but comfortable dress sandals would be a good call. Some of the actives may wear flipflops though so you could be ok, as I said, if they're "nice" ones.