I do not have any recommedation for the SD-card at hand.
But the idea connecting an USB-stick will not work with a PSoC5: The stick will need an USB-Host which cannot be done with a PSoC5.
Is that the same for external hardrive? im assumming yes.
Like i said just looking for suggested solutions to look into and possibly try.
I found a few SD shields on sparkfun that i assume will work?