This isn't even a challenge for me because I always make sure the product I have is almost gone before I purchase another.
Since yall are doing this challenge, just be aware of how fast you're trying to get rid of the product. Don't really be in such a rush to want the product to be gone so fast because if it goes fast, your money will go fast also. As long as you are getting enough of the product when you use it, don't worry about if something is still in the bottom of the container. I used to be just like yall, buying 3 or 4 of the same products and then buying more on top of what I already have, now at times, I just buy like 2 of the same products, instead of buying in bulk all the time. I have to get in the habit more of saving my money because I am a shopoholic. So good luck with the challenge.