It depends. Is the organization a qualified charity under Section 501(c)(3)? If so, you could potentially deduct your expenses as a charitable contribution to the team (organization) if you itemize your deductions.
Per the IRS, "the types of expenses that you may be able to
deduct include:
- air, rail and bus transportation,
- car expenses,
- lodging costs,
- cost of meals, and
- taxi or other transportation costs between the airport or station and your
hotel.
You can deduct other out-of-pocket expenses as well. According to IRS Publication 526, to qualify for a deduction, the expenses must be: "Unreimbursed; Directly connected with the services; Expenses you had only because of the services you gave; and Not personal, living, or family expenses." Bringing items from home to let the team "borrow" wouldn't qualify, but if you bought equipment specifically for the team, that would be deductible.
Here is some additional information you may find helpful: Tax Tips for Coaches