Husband carries the keys {as he would NeVER, under most circumstances let me drive and that's FINE with me} and cell phone. I carry a little wristlet with my make up for retouches. That's for an evening out.
If it's a shopping type of expedition--I carry my phone and bag.
We both usually bring everything. The few times I haven't brought my stuff, I wanted to go somewhere else and then walk home separately and then couldn't do it! But if we are going out, I may carry his wallet in my purse, or I may put my stuff in his pockets if I don't want to carry it.
It depends on where we're headed. A quick trip to the grocery store I won't bring anything, a longer venture I'll likely have my wallet, he ALWAYS has his.
We both bring everything. I guess it's habit from when we weren'tiving together and needed our separate key- as for phone amdwLlet I bring them with me always just in case.