I've been a SAHP/housewife for 15 years. Others have talked about the importance of own money/pensions/NI credits etc. In our case, DHs wages go straight into our joint account and I manage the money. We check any significant purchases with each other. I keep our savings roughly equally split between the two of us. I pay into a pension for me, directly from DHs salary in the joint account. More generally, DH still shares household chores, took the kids out alone when they were younger and encouraged me to get out and do things for myself (including weekends away), to have a break.
What has changed over the years is my realisation that despite this seemingly perfect SAHP set up, I'd still be fucked if we divorced. When I stopped working, my PT salary was more than DHs full time salary. Now, DH earns a good wage but if I had to support myself I'd be looking at part time minimum wage, because of heath problems and that I'm still a carer for DC3. I've also lost confidence, not having been in work for so long. So if we divorced, he'd still be fine, able to afford to live and keep his savings intact, whereas I'd be having to start again at the point I'm the least able I've ever been, and having to use my savings to supplement my income/house myself.
With hindsight, I would advise anyone now that if possible, to try and keep at least a toe in work (1 or 2 days a week would be fine) just because it gives you options. You have something for your CV, you have references, you have a much better chance of being able to start again, should you need to, because you don't know what life is going to throw at you.