What do you buy?
I'm mostly a Couch Potato kind of investor, so I just buy VBTLX. If I had a high enough marginal rate, I would buy VWIUX.
What is your target bond and cash percentages for the day you fire?
I don't remember the timing, but around the time I FIREd, I was at 100% stocks. Sometime around or shortly after FIREing, I went to 90% stocks 10% bonds because I wanted to maximize historical safety over my 40 year planning horizon. Later I realized that I had perhaps twice to four times as much money as I needed, so that morphed into my current plan, which is 90/10 for "my" money and 100/0 for "my kids'" money. Right now I'm at 98/2.
I've been at minimal cash for pretty much forever. Definitely less than 1% and probably rounding to 0%.
I have avoided bonds and have planned without them, but is now a good time to buy them?
I think you should have a well considered investment policy statement (IPS) that would answer that question for you.
How about preferred stock or the dividend aristocrats? How useful are these to ease volatility?
Preferred stocks and dividend paying stocks tend to be less volatile. Bonds are probably even less volatile than both of them on average. All three are going to be both lower volatility and lower returns on average.
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A somewhat common pattern is for investors to flee volatility into safety when things are bad, selling at a loss and buying at a premium to do so. When things turn around and volatile investments are doing well, they reverse the pattern and sell their safe investments at a loss and buy stocks when they are higher. Stocks eventually waver, causing the cycle to repeat. Note that these investors pay commissions, fees, and taxes on both ends of the cycle.
The previous paragraph is an excellent way to pay much more in taxes and be left with much less than otherwise. An IPS with an AA that reflects your true risk tolerance works better I think.