I usually bring $500 in cash and use credit cards wherever possible. Always go home with several hundred in my pocket. I do carry my license with me and I am frequently asked for id at grocery stores - never anywhere else. But if you are driving, you best have it.
For me, it's tee shirt and bathing suit during the day and polo shirt and shorts at night. Bring less clothing than you plan. There are pleanty of places to do laundry. BVI is very casual.
Like Evan, we avoid places that require long pants 99% of the time. On rare occasions, I will wear long pants for places like Peter Island, Biras and Little Dix. I just wear whatever I wore on the way down. For shoes, one pair of walkers and sandals.