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.
But transport of tomatoes is to high, well probably is not, but in future, will be more + people will just dont want their food travel half world.
Reality is, people from Uganda will get more interent jobs, since wil be cheaper to hire. People from Ohio will grow Tomatoes since they wil able to sell them expenciver. But reason for this is nto BTC, but BTC will help it to happen.