I have tested this a few times on different PC's. It seems you must have food in your inventory to be able to rest in the wilds. Even if you make a "Successful" roll where the food is then not consumed.
If you try without any food at all it is 100% failure.
I have been tracking this, just FYI.
I have failed 22 times in a row as a Druid, with 7 Wilderness Survival. Unsure if this is a bug or just a very high DC, or if I am extremely unlucky.
Been checking each time and to date my PC with now 8 on Wilderness Survival has never made a successful save in what must be 40+ rests in wild areas.
I am guessing something here isn't working as intended?
With 0 Wilderness Survival on a wizard PC I have occassionally passed the save. Might just be really really bad luck?
On a ranger with 5 wilderness survival, so far I had like 60-70% success.
After cranking Wilderness Survival to 10 (Ranger L5) for the following 4 rests I failed and used rations. (100% failure).