There's a good book called Natural Navigator by Tristan Gooley, you could have the character pick up some of the tips and tricks in the book organically to build their internal compass, a month of observation would develop some good skills.
If they need to get to a particular point on the river (Food Cache?) there is a trick to getting to a point on a linear feature. Say the river is running north to south and you head east from a particular point. On the return if you guess where west is you will either end up upstream or downstream from the point you left, meaning you don't know to turn left or right to get to where you need to be. If you take west by south or west south west on the way back you know for certain when you hit the stream you will be downstream of where you need to be and you know to turn right and travel upstream to the point of departure.
