...you can buy a "USB On-The-Go" cable adapter that allows the A70b to switch into host mode. I have one of these and can report success attaching mice and keyboards. I have not been able to get any thumb drives to work (although other people have), the reason being that the A70b will only supply 100mA of power and most USB devices require more than that.
There seems to be something else going on beyond just power limitations because I own 3 Archos devices (actually more, but won't get into it here)... a 70b (with Honeycomb), an 80 G9, and a 101 G9. And, I also have about half a dozen different USB Thumb Drives from various manufacturers.
I have noticed that the 70b does seem to be much more nit picky, but also does not like to connect to a USB Thumb Drive (via an OTG cable to the microUSB port) if a microSDHC card is also already plugged into the device. Almost seems like you can only use one or the other at a time. I think the "mass storage device" drivers may simply not be set up to work with both at the same time.
Oddly though, I can plug in a USB mouse and it does seem to work with a micro SDHC card plugged in.
And, between all 3 of my Archos tablets... what's really confusing is that sometimes my older Thumb Drives (that need more power) work on one or another, while my newer (lower power) Thumb Drives still do not work on all of them. So, it seems to be hit and miss kind of situation to find any USB Thumb Drive from any specific manufacturer that works with the Archos tablets.