Can you wait and buy it when you arrive? NO
By radio,we mean something to receive music etc, not a two way communication system. That sort of thing can land you in trouble in many African countries.
Radio is useful as entertainment,whilst waiting for busses, on long bus trips, airplanes, stuck indoors with sun stroke, or relaxing to your favourite music whilst you admire the views. It also helps with local news and weather, and world events that may have an effect on your holiday.
Some mobile phones and most mp3 players have a radio built in, and there are mini radio sets you can buy which are no larger than a big cigarette lighter. They can be battery powered, solar powered or wind up.
What you take is mainly dictated by cost and bulk - but you should also consider durability, weather resistance, added features such as being part of a phone, or having a built in flash light etc.
If you plan on leaving your radio behind with a host family or Ugandan friends, then go for a wind up one, or as second best a solar one. Batteries are both scarce and expensive in Uganda.
A wind up or solar powered radio with a socket for charging mobile phones can provide a villager with an income and bring in wealth to a village!