If you don't feel like changing the image of course, OpenWRT does also support samba with a Luci add-on to allow easy and convenient configuring. AFP is also available on OpenWRT but not so easy to use, and i think NFS is as well though samba is probably the easiest and more widely supported, however all these are documented well on OpenWRT wiki.
Basic instructions if you want to use OpenWRT:
connect the vocore to the internet via wifi as a client in OpenWRT make sure you use Scan to find your wireless then click join, and on the next page,
untick 'replace configuration' when setting it up so you don't lose access to the vocore, and assign the
LAN firewall prefix down the bottom before submitting the configuration.
(i've found the vocore supports working in client and master mode at the same time)
once connected, you can update the package manager (
opkg update from command line) and install the packages
samba36-server and
luci-app-samba opkg install samba36-server luci-app-samba
and when it is finished you should find "Network Shares" under the services menu in Luci
As for the USB stick, i recommend either keeping it as Fat32, or if you need files larger than 3.9GB, format it to EXT3 or EXT4,
In Luci, go in to System > Mount points, and you can mount your USB drive there, it should show up in the dropdown for available devices, and you can choose a mount point such as
/mnt/usb or whatever you want (as long as it's under /mnt/), if you want guest access to work, enter 777 in the create and directory access boxes and tick allow guest access, leave allowed users blank.
then enter the same path in to the samba configuration when adding a new share.
(if you run in to issues creating folders, try chmod -R 777 /mnt/
your_drive in the command line)
Hope this helps
comment back if you need any more info or help
More detailed instructions for using Samba on OpenWRT