Unfortunately there is no one answer for this.

We wanted to provide a general configuration that is a good starting point, we enabled a generous set of utilities to help people get started.
Also we've enabled extra components of the kernel to allow for things such as mounting ISO CD images in loopback, NFS, SMB (windows shares), etc.

You could try to modify the configurations (both kernel and Linux) to remove components/utilities that are unneeded by your application. If you don't need network filesystems or compact flash, you could reconfigure the kernel to remove the following network filesystems (turn them off, not just turn to module):

NFS
SMB

adn int filesystems, turn off the following:

ISO9660
VFAT
MSDOS
second extended support (EXT2)


This will save some space in the kernel.

You could also try removing merge/usr/lib/iptables and remove ipsecadm from the linux (not kernel) configuration uner 'userland applications' and rebuild after a 'make clean' to force a complete rebuild of the kernel/root filesystem.

What type of application are you trying to put together? I.e. what components of the root filesystem do you need?