I don't buy bonds or CDs -- I'm young enough that short-term loss is a non-event, since nothing short of "my children are starving on the street" will induce me to touch the Roth ahead of schedule. Wild volatility doesn't matter because I only check the account about once a year anyhow -- the only concern is maximizing expected 40-ish year returns.
I generally try to keep a few thousand in cash to cover unexpected expenses, although my discipline with that has left something to be desired as of late. (I'll say this for being a salaryman: I never had to deal with wild swings in my paycheck, and haven't quite mastered the trick of doing so yet.)