It's never a bad idea to have spare parts for your MakerBot lying around.
I have an old batch 2 MakerBot with outdated z-guides which make removing the z-stage really difficult. Luckily the new version of the z-guide is super easy to print out.
Also interesting is the x-rod bracket. Upgrading to the newer, skinnier rods is a little easier now and you need four less lasercut parts.
Yay. Hardware upgrades over the internet!
If you want to make any of your own parts the dxf's are all online (or in the repository http://svn.makerbot.com/).
Print! (I suggest the z-guides if you have an oldie like me).