It sounds like you can definitely skip fenders, and depending on the length of your ride a rack...

I use a rack because I like long rides with a snack/picnic along the way, plus more tools and emergency supplies than most people carry. My paranoia is based on the fact that I like riding isolated rail trails, and I can be up to about 7 miles from the nearest trail head, and in some cases, the nearest trail head is a long way from significant civilization. So, I could be up to 12 or 13 miles from the closest help... That could lead to a 4-5 hour walk pushing a disabled bike if it happens at the wrong time... so I ride over-prepared.

Also, unless you are the fastest rider on a trail, a mirror comes in handy on a trail too. It helps you spot riders coming from behind and be prepared for them to pass by moving over to the edge of the trail.