It's nice that Samsung brought back the microSD slot, but for the dual-SIM versions of the Galaxy S7 and S7 edge things haven't changed really - the hybrid slot means you can have either two SIMs or one SIM + one microSD, never three cards at once.
You know what they say, never say never. With some scissors, a lighter and a lack of caring, you can do this ill-advised hack - if a microSD and nanoSIM can't fit in the same slot, you make them fit.
I'll leave you to read the gory details over at NoReplied.com, but essentially you cut around the metal contacts of the nanoSIM and glue it to the microSD. If you manage not to kill the SIM while cutting it and to then glue it precisely in place, you'll get extra storage and an additional phone line!
Or you'll be out a nanoSIM card, maybe a microSD too.
I got one of these which works like a charm... https://www.youtube.com/watch?v=xp_VoNfonng
Better to use an external Triple SIM adapter like SIMore G2 BlueBox http://www.simore.com/en/dual-triple-sim-card-adapter-bluetooth-android-g2-bluebox.html Video demo with Samsung Galaxy S7 edge: https://youtu.be/4hr0bOKiXAQ
If you travel a lot may be you should consider switching to Truphone. check it out.