Kenyan beer is decent. There is one major brewer whose flagship brand is Tusker Lager. Also try the Tusker Malt Lager. Another good lager beer is White Cap Lager. Imported beers are available in supermarkets and better hotels, but the prices are usually high. But imported Tanzanian beer like Kilimanjaro and Safari tend to be cheaper than even Tusker. In local bars, do not expect to pay more than around 150 Ksh for a bottle; anything more is a tourist rip-off.
Imported and local wines and spirits are widely available, and it is advisable to avoid local brews such as "changaa" and "busaa," which are illegal, unhygenically brewed and whose consumption has led to deaths on many occasions. It may be helpful to remember that "changaa" literally means "kill me quick" before deciding whether or not to drink a proffered glass of the beverage.
There is an excellent selection of soft drinks especially from the Coca Cola stable, but try the Tangawizi brand of ginger ale.