Answer:
There are flash drives of different memory capacities, ranging from 512Mb to 16Gb available in the market. What you will prefer will depend on how much you want to spend on a flash drive.
If your use is only related to storing text documents and other simple files without a lot of graphics then a low memory flash drive would be sufficient.
If you want to store a lot of music or videos then you would have to choose a flash drive with more memory capacity.