11 CFR 100.79: Unreimbursed payment for transportation and subsistence expenses.

(a) Transportation expenses. Any unreimbursed payment for transportation expenses incurred by any individual on behalf of any candidate or any political committee of a political party is not a contribution to the extent that:

(1) The aggregate value of the payments made by such individual on behalf of a candidate does not exceed $1,000 with respect to a single election; and

(2) The aggregate value of the payments made by such individual on behalf of all political committees of each political party does not exceed $2,000 in a calendar year.

(b) Subsistence expenses. Any unreimbursed payment from a volunteer's personal funds for usual and normal subsistence expenses incidental to volunteer activity is not a contribution.