OH and I each have separate incomes and own bank accounts, cards etc, but we basically share all spending and evedy month or so we sit down together and do a joint accounting to make sure we can afford all our spending between us. This does require trust and honesty, I do not feel the need to have my own secret stash of 'running away money' just in case, as was the case in a previous less trusting relationship.
We each have grown up children from before our marriage. When we marrried we sold both houses and bought jointly. At the time we made a list of all capital, investments etc and agreed the percentage we each brought into the equation. Our wills set up a trust on the death of the first which puts house, money etc into the trust for the benefit of the survivor. Trustees are the survivor and the eldest child of each of us. On death of the second of us, the trust is wound up and his percentage goes to his two children, my percentage goes to my two. Percentages can be amended if one of us inherits a sum of capital for instance.
Sounds complicated, but was vedynimportant to us both that it should be totally clear to the children that our marriage would not make them lose out. OHs mother died when he was a child, father remarried and eventually left all to his second wife, who in turn left all to her own children. OH still very bitter about losing everything that had been his mothers, and that was 30 years ago.
Think the most important things are trust and honesty.