If you sell other products besides just soap, you can give bars of soap out with purchases of certain amounts. I do this. For instance, for every $25 spent, they get a bar soap. I let them pick a bar of soap off this one table. I put my bars out there that either did not sell for me or did not turn out looking like I wanted from looks to the way the scent held. You can also cut the bars smaller to have more. It helps me to get rid of soaps fast, and it introduces customers to my soaps that might not have otherwise tried them. It also lets those faithful soap customers of mine get more soap. I get a ton of repeat soap business when I do this.
Also wanted to add: This is not really a promotional offering but you check with groups in your area that might need donations for raffles, silent auctions. Not just schools, but animal shelters, victim advocacy programs youth organizations, veterans organizations, any program or organization that helps your community, etc. It is all about supporting your community. You can donate a simple bar of soap with a cheap (in cost) sponge or scrubbie. or 2 wonderful bars of soap. Not much money out of your pocket. You help out the group or organization, get a tax deduction and get your name and product out there at a low cost to you. Often when you make donations to organizations such as these, they will run a 'Thank You' ad in the local paper listing the sponsors and donors. I know I am a person that will make a conscientious effort of supporting a business that I see supports my community.