Take small cord, about 1/2 the diameter of the hanging rope. The aircore guyline cord sold by BPL works great. Cut 2 lengths about 8" to 12" long, experiment for what length works for you. Tie the two lengths into 2 loops, maybe using overlaping overhand knots. Using the loops, tie prussik knots on the hanging rope, one just below the other. Get 2 small twigs, say 1/2" in diameter and a little longer than the width of your hand. Girth hitch the twigs to the prussik loops. Use the twigs as handles to pull the rope - much easier on the hands - spreading the force across the width of the hand. With the 2 prussik loop handles on the rope adjacent to each other, pull down with both prussik loop handles, hold rope in position with the bottom prussik loop handle and slide the top prussik loop handle further up the rope, hold there and then slide the bottom prussik loop handle up just below the top one. Use both prussik loop handles to pull the rope. Repeat. Reverse to lower the rope.
You can also get by with just one prussik loop handle. Just step on the hanging rope to hold the rope position when you slide the single prussik loop.
The two small cords for the prussik knots weight almost nothing and can be carried easily with the hanging rope - maybe just leave on the rope so they are always there. Pick the twigs up from the ground where ever you hang the bag.
Using the single pulley and 2 ropes will eleminate the friction on the top of the tree branch, but will give you no mechanical advantage. You would need two pulleys, use a double sheave and a single sheave to rig a practical pulley system. With those you can easily rig a system to give you a 3:1 mechanical advantage (the 60 lbs reduces to 20 lbs to you), but you will need a hanging rope 4 times the length of the top pulley above ground - in practice the hanging rope would need to be about 4 times the length of the rope holding the top pulley.