Always check “best before” when buying a bottle - some drinks are way out of date.
Avoid drinking tap water, even in restaurants. Bottled water can be found most anywhere at reasonable prices. Expect to pay 400 cfa for 1.5l in the major cities, more in more remote areas.
Coca-Cola is available everywhere. For something different try one of the flavourful TOP sodas. They are much sweeter than most European or North American sodas but they are very tasty.
Cameroon is rich with choice when it comes to good beer due to its past as a German and later French colony. Bottled Guinness can be found everywhere although in the heat, try one of the excellent lighter beers such as Castel, Beaufort, Mützig, Isenbeck, Satzenbrau or 33. These are inexpensive and excellent in the heat. Castel Milk Stout is an excellent choice for those who like darker beer. Outside of the cities you will sometimes be hard pressed to find them chilled due to a lack of electricity.