You should be able to document that the trip was primarily for charitable purposes and time for recreational activity was secondary. Any expenses related to non-church activity would not be deductible.
To be deductible, your expenses must be unreimbursed, directly connected to your unpaid church work and incurred only because you performed the unpaid church work. You must itemize your tax deductions on Schedule A in order to claim a deduction for your church work. You claim your deductible expenses as a charitable donation. It would be good to have an acknowledgment from the church attesting to the necessity of your trip to the church.
