For general supplies you're better off going to Mtwara but basics can be purchased in Mikindani. There are general shops duka all over town, the best of the bunch are probably the ones at the daladala stand.
Kuchele is the towns resident artist and has shop next to the old slave market. If you're in town more than a day he will probably find you to show you his work. He's a nice chap and won't switch on the 'hard-sell' if you look through his work.
The Old Boma has a selection handicrafts produced locally, but a better selection can be found at ADEA in Mtwara.
