Stuff they might want:
1. Smart phones. Especially iPhones. There are 0 authorized Apple stores in Tanzania. A black market certainly exists and second hand smart phones are around, but (probably due to the two-year contract renewals that come with new phones) they are still cheaper in the states. And the connectivity improvement that comes with having a smart phone in a country that mostly lacks landlines, service contracts and cheap computers but does have mobile banking and easy access to phone credit.... is huge.
2. Batteries, of all kinds. Long-lasting and high-quality batteries are also still cheaper in the US. Especially if your dad likes to buy the giant packs of AAAs from Costco.
3. Cords and cables. Also a quality issue. Computer cords and outlets seem to get a lot more element exposure (dust, rain, crummy outlets, playful children) in Tanzania than they do back in the states. I've come bearing two mini USB to USB cords to replace older frayed ones.
4. Tough ziplock bags. Clear plastic bags that actually keep liquid in or keep liquid out. I'm actually still reusing the same ones I brought in 2013.
5. Quality sunglasses. Well, this White-Person-with-Irish-Eyes needs sunglasses. It's not entirely clear if the average Tanzanian requires sun protection, but the dust in the dry season is up the wazoo, so sunglasses that don't break after 4 wears are extremely useful.
6. Good hairbands. The kind that are think enough to hold a big pony tail, don't have that painful metal doodad and don't break after one week. These are priceless.
Things to keep in mind as we navigate the SWEDOW flowchart. Any other suggestions?