<p>SD card or usb device - either 128GB or 256GB. However, you have to pick very carefully if you care about performance (specifically write speed). Unfortunately 'USB3' (for example) does not promise good performance. So do your research. If 128GB is not large enough you can by ssd 'backup' drives as suggested above. ssd can be more reliable over the long run IFF you buy the right models but USB are more common and have a lot of benefits. Personally my favorite is micro-ssd cards but don't know what sort of ports your laptop has.</p>
<p>btw how much space do you actually require ?</p>