What document serves as proof of travel expenses?

The correct answer is that receipts for lodging, transportation, and other travel-related expenditures serve as the official proof of travel expenses. This is because receipts provide detailed records of the amount spent, the date of the expense, and what the expense was for, which are essential for reimbursement processes within the Defense Travel System (DTS).

Receipts are also necessary for validating claims during audits or reviews since they provide documented evidence that the funds were indeed spent on necessary travel-related costs. The other options, while they may provide some level of information about travel expenses, do not offer the same level of specificity and formal documentation required for reimbursement purposes. For instance, travel itineraries and email confirmations are helpful for planning but do not document actual expenditures. Bank statements can reflect charges but lack the detailed breakdown of what was purchased and do not serve as stand-alone proof of specific expenses incurred.