How long is a piece of string. The number of songs you can store is dependent on a number of factors. One of which being the length of the songs themselves obviously.
The other is the bitrate used. A CD has a bitrate of 1.4Mb/s approx. This equates to about 10MB of storage per minute, ie 100 minutes on a 1GB memory stick. A mp3 file encoded to 128kb/s uses about 1MB of storage per minute, or about 1000 minutes for your memory stick.
If you are a fan of 70s prog rock that probably equates to about three tracks

But for an average pop song of say 4minutes duration that means about 250 songs on a 1GB stick.
To get 1000 3 to 4 minute pop songs songs on a 1GB stick you would need to encode at something like 32kb/s which I would not inflict on my worst enemy (I'm sure it contravenes the Geneva Convention on torture

)