What is the definition of "immediate"? 1 month? 1 year? 10 years? (assume I will be 10 years away from SS)

Maybe 6 months? I would not call one year or 10 years immediate.

Some things I am considering
1. Holding CASH (the easiest, probably least optimal strategy)
2. Holding a mix of CASH and Bonds and Dividend paying companies - enough to finance my lifestyle

Cash, definitely cash. It's not meant to be optimal, it's to be available in an instant.

Bad windstorm blew many trees down, two large trees across our driveway. Hustling good ole boys with chainsaws driving around in a pickup truck offering to clear trees on the spot. Wanted cash-cash but would agree to take a check that they'd cash tomorrow.

We had our heat pump go out in the middle of a week of 95 degree days once. $12,000 but they would hold a check for a week. Not immediate but certainly urgent quickly.

Bonds are not cash, bonds pay income once a quarter. To raise immediate cash you have to sell them at whatever price you can get.

Dividend paying companies. A sub-optimal investment. Dividends come at the expense of total return. People tend to implicitly believe that dividends are free money. they aren't.

So I am considering what I think is referred to as the "bucket strategy"

Bucket 1 : Used to finance my lifestyle until SS hits (say 10 years)

First off, a high enough allocation to bonds to last for 10 years will be an huge drag on the overall return. The only growth will be the stock allocation which you have greatly reduced.

Second off, I did some serious spreadsheet work on this "bucket strategy" several years ago, after following a series of posts and articles about it. The articles were not clear at all on how to run it.

Here's the link where you can look at it and can download it to play with the parameters: dropbox.com - SPY Withdraw by CashBucket rules