Is it possible to wire switch outlet combo on switch loop?
Your switch on the left has the HOT Wire coming in to it. The two blacks - one of those blacks is a jumper to the other switch. 

The White wires are not neutrals otherwise when you flip the switch you would have a dead short between hot and neutral and your CB should trip!

The wiring violates code! 

The box looks like a DIY'er installed it - and that would explain the wiring.

Normally - your hot run would come into the box (3-wires black, white and copper in a jacket :  Romex wire) from the Circuit breaker panel or as part of a loop.  You would then have 2 sets of Romex (jacketed wire - 3 wires in a  jacket)  going out from that box to each light. 

Inside your box the whites would be tied together with a wire nut and the grounds would be tied together with a wire nut. 

You would have the hots (black wires) Black from CB panel on bottom screw of switch - with the black jumper to the bottom screw of the other switch, and a black from your outside light 1 to the top screw of switch 1, and a black from your outside light 2 to the top screw of switch 2. 

What this means is those outside lights are wired wrong as well - just looking at the wiring - as sharp minded Harper pointed out current is probably carried by the ground! - I would say he is right on point too - because a DIY'er went cheap with the wire runs - that is why those whites are being used as hots! Now I will bring up something else - the hot coming in to this box might be fed from another nearby circuit - near to the outside light or near to the switches there - either way probably SCREWY!

Now to add an additional outlet to that box as part of a combo - First FIX your wiring to be correct according to proper practices and CODE. Then you can put a combo switch/outlet in the place of one of those switches. You should be able to do this with 3 Romex cables - 1 From box to Light 1, 1 From box to Light 2, 1 From CB panel (or from a loop) to Box.