living in government quarters, and eating government provided food, so they don't get mileage, housing allowance or food allowance. There's a famous story from Apollo 11 that I read in Buzz Aldrin's book. After returning from their mission, each of the crew members filed a travel voucher. It went something like this:

Home to JSC airport by private car
JSC to Cape Kennedy by T-38
Cape Kennedy to Moon by Apollo spacecraft
Moon to Pacific Ocean by Apollo spacecraft
Pacific Ocean to quarantine by government transport plane
JSC to home by private car.

They got paid the mileage to and from the JSC airport in their private cars. Aldrin's book actually has a picture of the voucher in it. It's pretty funny.