Students should pay for their travel expenses and not those of other students when possible. If sharing lodging, inquire about splitting the bill so that each student can pay for their own share and so that you will have a receipt showing exactly what you paid.
If making individual payments is not possible and one student makes the full payment, you can still be reimbursed for your share of expenses. If another student makes the full payment and you pay that student for your share, you must submit documentation showing the full payment made and documentation of your payment to the other student. For example, a Venmo or Paypal receipt of your payment to the other student is acceptable.