Well it would buy the same, just like today i guess.
today you don't buy the same amount of... say.... tomatoes in USA and in Uganda, with 1 dollar. In USA people have much higher wages so they will pay more. In Uganda wages are much lower so even prices.
How would bitcoin deal with it?
demand from the USA will cause the price of tomatos to rise in Uganda.
once the people of Uganda see that the you can earn alot of money in the tomato business they will start opening more tomato farms increasing the demand for tomato workers,
this will cause the tomato worker's wage to go up as well as the supply of tomatos from all the new tomato farms.