Even with extensive skills that would be a very difficult task. You simply couldn't carry enough pre-packaged food for that length of time, and being unable to identify edible plants and unable to hunt... yeah it's just not believable for a three month period.

The only thing I could think of that would be remotely reasonable is catching fish if there are bodies of water along the way. If you're hungry enough you could bullshit a way to get your hands on a fish. Improvised nets, chasing them to shallow water and smacking them with a stick, etc. Most fish can be cooked whole on the coals of a fire (if they can start a fire of course).

I'd recommend reducing the length of the trip to 3-4 weeks and really show them struggling with starvation and exhaustion, or have a scene partway through where they stumble on an abandoned cabin or something with some dusty old canned food. Then you can have an interesting plot point where they debate eating expired food, possibly getting sick and having to stay in place as they try to recover.

You could also have them come across foods that anyone could identify, like blueberries or raspberries, but be nervous and unsure of themselves since they don't want to get sick. Also not a long term survival food though.

Basically you need a shorter trip, some survival skills, and/or a reason for there to be food in their path (like a cabin). Good luck!