The rainy season is in summer with a mild winter. South African Rands are accepted in the south as far as Vilanculos, thereafter it is advisable to take a supply of US Dollars or Sterling. Malaria is endemic to the country and precautions should be taken. In addition it is advisable to take precautions against yellow-fever, cholera, typhoid and smallpox.
Bottled water is advisable and is available, though expensive so it is best to take a a supply.
Also take along a supply of water purification tablets, just in case. Peeled fruit and vegetables as well as fish, chicken and the local baked rolls are delicious and quite safe to eat. Tinned foods are available, though once again expensive, so if possible take your own. Mozambique is a poor country and the inhabitants, though friendly, will relieve you of your possessions in the blink of an eye. Take reasonable precautions and don't leave your stuff especially photographic equipment etc, lying around.