Replacing attic light switch with Leviton combo
Romex 1 and 2 are using backstabs, which is not a good idea for other reasons.  

The backstab is simply connected to the screw nearest it, internal to the device.  It's supposed to be an "either-or", but some people like to use it to splice the 2 wires together. 

It would be the same as if the two wires were joined at a wire nut, with a pigtail from there to the device screw.  That is exactly what you should change that to.  

On a switch

One side is always-hot, and the other is switched hot to the lamp.  There would be no reason to have 2 cables feeding switched-hot.  Unless you had 2 lights. 

It would be very common, however, to have multiple always-hot wires in a box; the second one would be going onward to other loads.  

The grounds are nutted together ordinarily.  The neutrals likewise, you may be adding a wire to this neutral bundle to power the smart switch.  

How I would hook it up.

First I would get some red electrical tape and mark the wire to the lamp with red tape.  

A switch-outlet hooks up exactly like a smart switch, but without the convenient pigtails.   So I would make pigtails.   

Get about 7" of 12/3 cable.  14/3 will work if you are sure all the wires in the box are #14. Tear off the sheath to salvage the wires.  Then: 


bare wire to the green screw
white wire to the silver screw
red wire to the brass screw right next to the silver screw
black wire to one of the black screws on the other side


Then I'd join all the wires color to color, remembering you marked the lamp black wire red.  Normally you can't count on wire color codes, but I made it work here.

There are more efficient ways to do this, but they are not as clear.