In Sweden the tax authority provide a table mandating per diem per location (Socialism at its best).

It ranges from 30 USD / day if you find yourself in afganistan?!?! to 120 USD for the sudan....

Places you might actually visit work out somewhere in between there;
India and China are around 50 to 60 USD, Japan is 100 USD.

Other places I have worked have simply refunded reasonable expenses.

For the per diem, technically you are meant to account for the fact you paid for three meals a day yourself, but in practice I have never heard of a check actually happening.