State law is really important if the relationship fails and you need to split commingled assets. If that's something you're worried about you should speak to an attorney.
To directly answer your question, we both direct deposit into a joint checking account. We spend on cash back credit cards that are auto paid out of the joint checking account each month. Mortgage and car note are out of the joint account. We both maintain access to small spending personal accounts/cards on the side for gifts and misc. stuff we don't want to discuss.
When the checking account gets over our healthy buffer of ~2-3 months spending, we sweep the extra to a taxable brokerage account and invest it in index funds.
We "pay ourselves first" with prediscussed, significant, automatic contributions to retirement savings, college funds for kids, or any key milestones like down payments or big vacations. that way any money that stays in the checking account or misc accounts are relatively guilt free and discretionary.
Of all of the things that I mentioned, contributing to retirement and big milestones before we can "touch" the money has been the most important for our peace of mind. we don't fight over money because we've already aligned on the big stuff.