I use a Versus case, because I hate carrying a wallet.
The little slot in the back can hold two cards and two bills, which is all I need.
This is for a Note 4, but the S6 version looks the same.
I can't post links yet, so put the two below url pieces together, lol
veruscase.com/product/smart-phone/ damda-cases/verus-samsung-galaxy-note-4-case-damda-slide-series.html