Here’s a humble suggestion I have used:
When you get off the trail to hitch/walk into a resupply town or maildrop location - take along some 40-50 pound test fishing line (more like braided filament), tie it around a rock, or other heavy object, and throw it over a secluded tree branch. Haul your pack (should be relatively light since you are out of food/supplies) up toward that branch, out of sight, and tie the line off.
Should be safe from 2 or 4 legged bandits - just remember where you left it! I’ve used this method to cache storage containers in trees and it works pretty well. You won’t be gone that long and most critters can’t climb along a fishing line. Try keeping it about 15 feet above the ground and about 5 feet below the branch.
Brutus