It is not possible to read and write to external memory cards from an iPad, at least not in any meaningfully useful manner.
I'll go along with the "any meaningfully useful manner" , but I have a Mobilite gadget that takes SD cards and USB sticks, then transmits their data via a WiFi signal to the iPad, but it is "read only", no editing or adding to the SD card any data from the iPad, but better than nothing, i.e. I take all my passwords on an encrypted stick, so at least I can get into sites that need complicated passwords, and names of ones' Grandmothers first dog, to access when I am away from home and my 24 page A4 file of passwords and memory stuff, that one needs on a daily basis these days.
LIFE was easier before computers.