Luggage and bags: Bring your own impregnated mosquito net. You will be able to buy mosquito nets at almost every duka, but chances are, they wont' be impregnated with GAO (toxic mosquito repellant) and that's really crucial. Furthermore, if you go camping or to some of the non-touristy parks or guest houses in the cities, there won't be nets. And I can't say this enough - you should ALWAYS, ALWAYS sleep under a net. It's the best protection from malaria
Luggage and bags: Finding the toilet in pitch darkness can really be annoying so make sure to bring a really good flash light. Power cuts are really more the rule than the exception in Tanzania, so be sure to have a flash light next to your bed. Especially in rural areas, these cuts can last several days, and as it gets dark around 7 it's really nice to have a torch at hand.
Luggage and bags: I'm sure you already know this, but remeber an adapter, as the sockets look quite different from the European. Also, if you plan on staying for a long time in a rural area, consider bying a stabilizer to save your computer from the electric spikes. They can burn down your computer completely. Can be bought in Dar, Arusha and perhaps even Mwanza