It doesn't matter that you are clergy in this case, since you don't have clergy income to deduct expenses against.
You can deduct out of pocket costs for work you perform for any charity like any other persona and any other charity. In turbotax, enter your church's name under donations to charity. Add money donations for any money you donated. Add item donations for anything you paid for that was not cash or checks given to the church (flyers, supplies, etc.) For each item donation enter the date, say "I will value the items myself", describe the item, its cost, and choose a method of determining value (actual price.) You can probably summarize with one large entry of similar items. If audited you will need receipts and some kind of written statement from the church acknowledging your donations. See this for more, <a rel="nofollow" target="_blank" href="
https://www.irs.gov/uac/about-publication-526">https://www.irs.gov/uac/about-publication-526</a>
Unfortunately you can't deduct gas cost directly. The only way to deduct car expenses is to use the mileage method and deduct 14 cents per mile. You will need a record of the date of each trip, purpose, and mileage. This may not come up to gas cost, unfortunately Congress set a flat rate for charity mileage instead of an adjustable rate based on inflation and they haven't updated it recently. Enter the total number of miles driven as a mileage donation under charity donations.
If, at some point the church starts paying you a salary, then you can deduct these expenses as work expenses instead of charity donations. But that deduction has other limitations that will have to be taken into account at that time.
