I've recently started thinking about our finances in this way.
I love Our Next Life blog, and they've basically split their FIRE funds into buckets.
https://ournextlife.com/2016/02/17/how-we-calculated-our-numbers-for-each-phase-of-early-retirement/After giving it some thought, I decided that I liked it and I'm doing the same... mentally, at least. Right now, FIRE is still far enough out that my asset mix in all of my investment accounts is the same, but I'll change it as I get closer to the start date for using each type of account. I mainly just like mentally separating out traditional vs. early retirement.
The first bucket is "traditional retirement." I include all "retirement" accounts in there - 401k, Roth, whatever weird letters/numbers represent my husband's church retirement account, etc. I plan to start drawing from that pool at 58.5. (The first year will be Roth contributions.) So my spreadsheet tells me what the retirement bucket will be worth at 58.5 years old (assuming 7% gains) and what my 4% SWR works out to be. I'm 39 years old right now and that number is doable-but-very-lean right now, so we're no longer maxing those accounts but we're still contributing.
My second bucket is "early retirement." I lump everything in there that isn't an age-restricted account - cash, taxable investing accounts, HSAs (I save all of my receipts and therefore could get most of that money back easily). My spreadsheet currently reflects us starting to pull from that at 52yo, though we're currently not anywhere close to that being a number we can live off of. That's the goal, though. Right now, if we didn't add anymore, we could hit lean FIRE when I'm 57.... so still lots of work to be done. Focusing on that bucket right now.
I know that you can do Roth conversion ladders and all of that other stuff to address the early part of early retirement, and I'm sure we will do that to some extent (since I'll never want to forego a 401k match, I suspect we'll overshoot by a good bit), but I like having a backup plan in case Roth conversion ladders ever go away, and I like having this money mentally separated so I can mentally check off periods of our life as we cover them.