ok took slightly longer than anticipated, but 32 minutes later and here we go

i managed to kind of replicate your flash drive

i've colour coded the shell bits (the orange bits are the robot parts that get hidden inside the flash drive when in flash drive mode)

the legs are pretty simple, they just pull down and undo a few times to give articulation to the joints
the feet (which i didn't properly block out now that i think about it) are made from the bit that inserts into the computer

unlike the feet the arms don't follow a linear path for transforming... well... they can if you want but it will seem funny i think
they just curve down to where they are (that probably doesn't make sense but you should be able to figure out what i mean from the picture i think)
the handle bits just came down because i thought it would be able to bring it's arms up into a t-pose properly if they aren't in the way

the forearms just fold out, however i think in this current state it would actually conflict with the shoulders but that can always change when you go into detail

the head is tiny compared to the body because it came out from the circle thing
i think to make it look in proportion to the body you'd make it fold out and expand, unless you say it's a morphing head in which case you can always scale it up in it's transformation. but more non-morphing transforming you'd want to make it expand like how the all spark in the first micheal baye movie un-expanded down from a big cube to a small one

hope this will give you a good idea on how you could do it.