get a super mini 128gb sandisk thumbdrive. stick it in there and forget about it. i'm currently using it. add an extra 128 juice to my exisitng 256.

@chokia
11 street

@neuromancerx
i'm not using sd at all. not sure if the speeds is fast enough. i'm using usb thumb drive. sandisk. regarding the protrusion part, it does protrude a bit, but it's negligible and won't affect nor need to make any particular adjustment. basically i just leave it there ever since i plug in. dump all movies and music in there. it add in a much needed extra juice.
Most importantly, we'll need to periodically organise our drive. No amount of memory drive is enough.

@gabriel.l
it's an option as well, but having need to pay extra for the adapter alone turn me off.

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for those who are interested i'm using SanDisk Ultra Fit CZ43 USB 3.0 128gb. i uploaded a picture for your reference, the price as well. it's RM 93 for 128gb. i'm considering getting an extra unit since my mba equipped with 2 usb ports. only hold back is, i'll be upgrading to macbook 12 next year and it only supports usb c. can't really utilise both units.