If you buy soap from your local lush, u could do what I do. I ask the lady to cut my 100g bar into 3 pcs. You don't want your bar to be too small too, it's going to be difficult to grab. They will also wrap them up individually for u with labels. I love it.
However if u are too shy to ask them to do it, u can always do it yourself. Here a mini tutorial on how to cut up your soap without any hassle.
I have most of my lush soap cut in stall so I'm going to demo with my Anderson soap.
First of all, we need a knife. It doesn't have to be very sharp. A cup big enough to dip the blade of the knife in and hot water. A cutting surface and some tissue.
Fill the cup with hot water and dip our knife into it. The heat on the knife make it really easy to cut the soap as it soften the soap when we cut across.
The hot water also dissolve the soap so it won't stick to the knife. You only need to give a rinse to your knife after u used it. Your knife can still be used for food.
Dip the knife into hot water for a while
Use a piece of tissue to wipe dry
Cut the soap like u cut cake
Dip the knife into hot water in between cuts to ensure u keep your knife hot
2 cuts and here is what u get:
BTW, this is how i store my soap...