The amount of matter a person is made of is the same in every location. The mass of a body is the sum of the masses of all of the atoms it contains. It's literally a number of particles so it's unaffected by differences in gravity.
Weight is different on different planets and on the moon because weight is a function of gravity. Weight is the force an object with mass exerts due to its gravitational attraction to another object. The force of gravity is:
`F = G(M_1M_2)/(d^2)`
where g is a constant, M1 and M2 are the masses of the two objects (person and planet or moon) and d is the distance between them. What would be different if a person traveled to another planet is the mass of the other planet, not that of the person. A body with its fixed number of atoms is more attracted to the earth than it would be to the moon if it were on the moon's surface because the earth is larger.