The best way to know what is current is to look in the svn at the patches directory svn.smallwall.org/SmallWall/freebsd8/build/patches/to see what is currently patched.
In the past, the following patches have been applied to the FreeBSD kernel source that was used to build early m0n0wall releases:
clock.c: fix writing the day of week back to the RTC (Soekris BIOS resets the date to 1-1-1970 if it's invalid - 0 is not a valid weekday as per the AT specification)
if_ethersubr.c: disable multicast warning in bridge code
if_xl.c: disable hardware TX checksumming
ip_input.c: fix problem with packets from dummynet pipes getting NATed again
ip_nat.c: fix ipfilter bug (only required for 3.4.31)
ip_output.c: reverse ipfilter/ipfw processing order
ng_pptpgre.c: reduce ACK timeout to 1 second, disable PPTP windowing
subr_diskslice.c: disable warning about partition size
They are available to download from http://m0n0.ch/wall/downloads/kernel-patches.tgz.