Slice up extra green onions and drop them into an empty, clean water bottle. Freeze. Then shake out the amount needed for your next recipe. Re-cap and freeze the remainder.
Pretty clever, seeing as how you usually don’t need as many as you buy.
Along with that tip is this one:
The next time you have green onions, don’t throw away the white root ends. Simply submerge them in a glass of water and place them in a sunny window. Your onions will begin to grow almost immediately and can be harvested almost indefinitely. Just use kitchen scissors to cut what you need for meals. Periodically empty out the water, rinse the roots off and give them fresh water. (The root ends need to be standing in water, but the cut end should be sticking out of the water.)
*The very next day you will see new growth! I am doing this right now. Mine have been re-growing for 3 days and their is significant growth!!