You don't have to worry, you can eat everything in Tanzania. Bottled water and sodas are available anywhere if you don't want to drink tap water. Shopping Handicrafts are very cheap in Tanzania if you can bargain. Half the asking price is often no problem getting to. Zanzibar has the biggest selection but the highest prices.
Spices are very cheap.
If you want the cheapest possible, don't buy them on a spice tour. Go to the market in Zanzibar town and shop around for prices. There are not many beggars in Tanzania. If you want to give them something, go through an organisation or through their parents. Don't give them any pencils.