The most common beverage in Eritrea by far is beer. There is only one state-owned brand in the country so there is not much choice, but it is quite good. Beer is consumed cold in Eritrea! Beer's popularity is closely followed by various soft drinks, and the most common flavors are as elsewhere in the world: orange, lemon/lime and cola flavors, produced by one of the most recognizable brands in the world. The same company that holds the beer monopoly also holds the monopoly on producing the local form of Sambuca, colloquially called "Araqi", as well as Vermouth and other spirits. International brands of the same spirits, as well as others, are readily available at most bars for a cheap price. Sophisticated cocktails are not known in Eritrea as of yet outside of the Intercontinental Hotel which charges a steep price. On a side note, there is an Irish bar in that hotel.
Traditionally Eritreans also drink the local form of mead called "suwa", which consists of old bread fermented in water with honey, as well as a sweet honeywine called "mies".
Tap water should not be drunk by foreigners. There is plenty of relatively cheap bottled mineral water, both carbonated and non-carbonated in Eritrea.
Cafes in some towns offer fresh fruit juices. Unpeeled fruits can be eaten or squeezed fresh by you. Avoid "ready-squeezed" juices as well as ice creams and all types of salads. Stick to bottled drinks and cooked foods.