Place up to two or three avocados into the paper lunch bag.
Add an unpeeled banana or apple to the lunch bag. Adding the fruit increases the amount of ethylene gas that will accumulate in the bag.
Roll the top edge of the lunch bag down tightly to seal the bag completely just above the items.
Set the bag aside on a counter at room temperature -- between 65 and 75 degrees Fahrenheit.
Check the avocados after two days to assess them for ripeness. If the avocados yield to a gentle squeeze, they are ready to eat. If they still feel firm, return them to the bag and seal it tightly again.
Remove the avocados from the bag when they feel slightly soft -- the ripening process generally takes between two and five days, according to the California Avocado Commission.