Yes- so much advice. First off, don't take small denominations of US currency. Denominations less than $50 notes actually have a lower conversion rate!!!
Don't take a bag that has wheels as it won't fit into the locker- and these are seriously small so follow the rules!!!
If you like shopping and extra activities, take more money than 300 pounds. Also, there are plenty of opportunities for ethical purchasing- there is a shop at the Equator cross-over where you can buy items with profits going to AIDS orphans- items are more expensive than elsewhere but you are helping local children.
When you visit the orphanage/school at Lake Jinja, consider "adopting" a child. I am finding it worthwhile so far. Also, the old woman in the village is a real character but watch out if she wants to check you out as a prospective wife for Duncan. She also sells some handicrafts and as older woman are very rare in Uganda, it is a nice way to support her (her husband is no longer alive).
Spend a lot of time in the genocide museum- ask your guide to allocate enough time. We didn't get to go to the Rwandan markets so also ask your city guide to take you there.