A CO2 or Halotron fire extringisher could work (or any fire extinguisher rated for electronic use). Some people have suggested a damp rag to smother small flare ups. You could also use wool, which is naturally fire resistant (100% wool, it was used in fire blankets). Also, a small water spray bottle could work for flare ups, as well.
Here are a couple threads you could look at.
http://community.glowforge.com/t/source-for-co2-fire-extinguishers/2044?u=joe