How can I organize my under the sink in the Bathroom?

I think you should take a look at my "Garage Storage Bins" right here on Hometalk. I use these same containers under my kitchen sink and my bath vanity. It is so easy to pull one out, find what you need and put it back. I get about 4 of them under my kitchen sink and it's like having 4 drawers. I keep the less likely to be used to the back and the frequently used items in the front two. So easy to remove everything for a quick wipe down and then badda bing, badda boom, everything back in place. All free from the local grocery.

Another idea is to mount a cabinet/cupboard with shelves on the Wall for the Smaller items. this could be mounted on the wall above the Toilet for the Toilet paper and other personal items.. or lotions and that type of stuff.. Baskets or buckets for the other stuff.. I have a old antique pie basket I keep my lotions and spray colognes in... right on back of the toilet tank until I get a shelf there..

First thing you need to do is pull everything out of there and evaluate. Combine like items into one box or bag (ie: all band-aids together in one box, two half empty hand lotions into one container, etc) and throw out what you don't use, don't like, etc. What I did with my disaster area, was to find a nice plastic box with a snap top and I made a first aid kit. I put all of the bandages, alcohol, iodine, gauze, etc into it and now I store that in the hall linen closet, but you could put it back under the vanity if you need too. Everything else was placed in plastic baskets with like items. You could also use plastic shoe boxes with or without the lids. Easy to slide out to reach the back items. (I suggest plastics because of the leak factor under a sink). Be stringent when using items in the future to restore in the proper bin and don't just toss things under your sink when you are in a hurry. Good luck. Once it is done, that will be just one less stresser.

Each member of our house has their own bin under the sink. That organizes each person. All first aid items are in one bin in the linen closet. Toilet paper is stacked in it's own area (within close reach for those in need ;-), sprays/detanglers/gels that are shared are in a separate bin, soap is all together, dental supplies also together and shampoos are in their own bin, too. Plastic bins are the organizing answer for me. Hope that helps!

Boxes with categories (per person or per type of item) make a lot of sense - and you could even repurpose cookie tins or shoeboxes and use contact paper to make them look nicer.

I agree with above, I use the clear plastic shoe boxes from the Dollar Tree. Organize and label by topic, like First Aid, Shoe Stuff, Makeup, Band Aids etc.

I have several organizing posts that might help you https://chascrazycreations.com/diys/how-tos/organizing/