So there are a few ways to get the soap you need. The way I did it was to go to Lush and buy these packs which have two slices in each. You can also go to shops that sell soap which is cut from wheel shapes or shops which will cut soap to any size you want - otherwise you will end up paying for a lot of soap you don't need. Don't worry about the exact size of the soap yet as long as it is wedge like.

here are links to the lush ones:

http://www.lush.co.uk/shop/product/product/path/136_141/id/764/handmade-showers-soap-beach-bars

http://www.lush.co.uk/shop/product/product/path/136_141/id/765/handmade-showers-soap-foam-a-friend

http://www.lush.co.uk/shop/product/product/path/136_141/id/761/handmade-showers-soap-ice-and-a-slice

http://www.lush.co.uk/shop/product/product/path/136_141/id/763/handmade-showers-soap-sweet-soap-of-mine

http://www.lush.co.uk/shop/product/product/path/136_141/id/762/handmade-showers-soap-top-of-the-blocks

Line up your soap wedges to find the best shape. Because these Lush ones are right angled, not icoceles in shape, they wont line up perfectly so try to get the best fit by trial or error. A good idea is to do this in the shop if possible incase you came home to find you didn't have enough. Mine took 13 slices as you can see.

Now take an appropriate circular shaped object like a side plate and using a knife draw around it into the soap.

Next cut the side of each slice so it makes a perfect cake shape all the way around.

Now decorate the box before you put the soap in it. I did mine with a slice of cake with bubbles on it as you can see! Good idea is to do this on a seperate sheet of paper and glue it on later incase you make a mistake.

You can also do drawings that are coloured of the different soaps inside as a legend for the person gettting the gift.

Now put the soap in the box and put your ribbon around it, affixing it tightly by tying it or glueing it or using double sided tape.

close the box and it's finished!