I may have missed this, but didn't see it in the sticky and is one of the most important things in my opinion.
Health insurance. What will your new insurance be? What will it cost? What doctors and/or pharmacies won't accept your new insurance?
I'm in the glide path to retire early next year and have been working from home for 2 years, with light work. So I have had the privilege of "pretending" to be retired. What I will do is figured out. The costs of insurance is still a bit up in the air. I have one son who just turned 26, so is now on his own work insurance. DW quit her job so there won't be a family plan for insurance. Younger son and DW will be on ACA and I would go on medicare. Still, because this year's income is going to be very high, both ACA and medicare will be expensive for the first year. So for those of you much younger than me, figure this out as it can literally cost you more than everything else combined. As a family, we will be going from $400 a month insurance cost to more like $2000 a month plus whatever my older son pays. Having worked for various companies over my career, we've also had various companies not have some of our doctors "in plan". Currently, Cigna is our network and of course, they have consistently been rated the WORST network every year. We've had to deal with that and pay out of network costs.
On the list, but worth mentioning is the sick pay and vacation pay. In my present job, if not used by the end of each year, my company zeros these. If you leave, you get a check for zero for these. I just want you to understand that this is not all that unusual, so if you've saved up 10 weeks of vacation and "assume" the company is going to give you a fat check, you'd better be sure. If your company is like mine, then putting in for vacation to use up the days, then making your resignation after all your vacation time is used is the way to go.
Something also missed is house repairs. We are currently in a string of house maintenance and I'm glad we're doing it while I'm still working and bringing in big RSU, ESPP and bonus money. First, we replaced dilapidated garage doors for about $4800. Then we had a retaining wall that lines a stairway into our basement as stones were literally falling and that cost $4200. Currently our house and garage are being painted with a separate carpenter in replacing any rotted wood (and there's a lot) which is $10k for paint and $3580 for carpentry work. We had the roof replaced 2 years ago for $15000. We do have plans for some reconfiguration of floor to ceiling windows that are leaking and are 35 years old, so that will be done in the spring. Plus a couple bathrooms and an office to redo and as the carpenter found, one wall has water damage so he'll get to it in the spring. All of this, once done will likely exceed $100k and if you have similar work that needs to be done, that could really be a hit on your budget. Maybe you're renting or your house doesn't need repairs, in which case, ignore this.
I disagree with car replacement. If your car is running, I don't care if it's old or has high miles. Sure, if you'd take out a loan, it would be harder to get with no income. But these days, with skyrocketing car prices, it makes sense to repair nearly any car. We repaired our 2013 Subaru Crosstrek, maybe a year ago. I had received a car max quote of $2800 for the car. But I looked and had thought that I'd do what I had done in the past, getting a car that was maybe 75k miles and 2 years newer for maybe $7k or $8k. Nope. A 150k same car, 2 years newer at a used car dealer is now $17k. So our car got repaired. It has the infamous Subaru CVT problem transmission that Subaru replaced under warranty at 53k miles. So at 150k miles, the common solenoid control module ($800) needed replacement. We had that done, a ball joint, a wheel bearing (the other 3 had been replaced already), and both front CV axles. This was about $2500. Nearly what car max would have given us for the car. In addition, the tires were spent and needed replacement, so that plus an alignment was another $700. All this was done at 150k miles. Well, since then, my younger son has been driving the car and goes to welding school 4 days a week which is an hour and a half drive each way. So we just did the oil at 175k miles and the car drives fine, so I feel we made the right choice repairing it. Over this past weekend, he told me that the windshield wipers stopped working. We did a little diagnosing and internet looking and figured out that the motor was toast. Off the the pull-a-part junkyard with a small tool bag and we pulled the assembly out of an Impreza and he installed it in the car. So a fun hour in the junkyard and $17 and it's fixed. Heck, while I was there, I also got the little plastic pieces that cover the wiper bolts as one had been lost. Win!
I also highly recommend you make a "retirement spending" list. This is everything from health insurance through car insurance and homeowner insurance to grocery store, restaurant, travel, gas, heating oil, electric, cable TV, internet, car repair, tax and inspection. Everything. I started making my list about 5 years ago and every year, I fine tune and add things. My list started as under $50k a year and is currently about $67k a year and far more accurate. You want to know your costs before bailing from your paying job. You can use this for your 25X, where the list is your X. That's only a rule of thumb. Long ago, I made a life spread sheet with assets, income, spending charted by each year. I put in 5% as growth of each year's assets and as the year ends, replace predictions with real numbers. What I like about doing this is that we could put in expected college costs for the kids, new roof, new cars, all the little one-time cost things. It's also good at predicting each year what we'll spend and have. From each year, you can hone in and even change future costs. For us, college went up more than expected annually but the kids' grandparents made contributions towards college, which was completely unexpected and really appreciated.